HYRUM
Filled before it was approved
A 1935 relief project that stored water four months before the President signed off on it, built as two structures rather than one, and surveyed twice with results that do not behave.
Hyrum Dam was authorised under the National Industrial Recovery Act of 1933 and paid for by the Public Works Administration in August 1933 . Then the dates go out of order.
| Date | What happened |
|---|---|
| March 1934 | Construction begins |
| 1 April 1935 | Closure. The reservoir starts filling |
| July 1935 | First water delivered to farms |
| August 1935 | Construction finished |
| November 1935 | Presidential approval of the project |
The whole thing went from an empty hole to delivering irrigation water in a single season. Closure on 1 April, water on the fields in July.
What it was for, in Reclamation's own sentence: the project "stores and diverts water from the Little Bear River to furnish supplemental water supplies to 6,800 acres of privately owned and cultivated project lands" . Note supplemental, and note already cultivated. This was not built to open new ground. It was built to cover a late season shortfall on farms that were already there.
The contract went to J. A. Terteling and Sons on a bid of 337,221 dollars . That is the dam only, excluding the canals, the pumping plant, land and engineering. No total project cost was found in any Reclamation document, and the project history that would carry it is a scanned PDF with no readable text.
The dam inventory returns two records under the identifier UT10123 . They are not duplicates.
| Hyrum Dam | Hyrum Dike | |
|---|---|---|
| Identifier | UT10123 | UT10123S001 |
| Height | 116 ft | 18 ft |
| Crest length | 540 ft | 850 ft |
The dike is longer than the dam and a sixth of its height. It closes a saddle on the rim about 433 metres east, where the reservoir would otherwise spill out of its basin.
And neither dam inventory record is called "Hyrum Reservoir." They are filed as Hyrum Dam and Hyrum Dike, with the reservoir name appearing only in the other names field. A query for the plain name finds nothing.
Reclamation has surveyed the bottom of this reservoir twice and published both results . The numbers do not move the way anyone expects.
| Survey | Capacity at elevation 4,672.5 | Change |
|---|---|---|
| 1946 | 18,685 acre feet | the published design figure |
| 2006 | 17,746 acre feet | down 939, over sixty years |
| 2018 | 18,221 acre feet | up 475 |
All three numbers are Reclamation's own. If you want one current figure it is 18,221 acre feet from the 2018 survey, and the 18,685 that Reclamation and the dam inventory both still publish is the original design capacity.
Note what the surveyors were working with. The 2018 survey was run on 29 and 30 October with the water surface between 4,651.77 and 4,652.03 feet, about twenty feet below the reference elevation . So Reclamation measured a drawn down reservoir and extrapolated up to full pool, which is ordinary practice and is why the report's tables run in tenth of a foot steps from 4,600 to 4,673 feet. The report publishes no sediment volume and no sedimentation rate, so this page gives neither.
No agency source publishes a maximum depth or a mean depth for Hyrum Reservoir. Not Reclamation, not the dam inventory, not the wildlife division's survey, not the state park. The one document that would obviously carry it, the bathymetric survey, does not state it as a figure .
Dividing capacity by surface area gives a mean depth of 39 to 42 feet depending on which pair of published figures you use. That is this page's arithmetic, not a measurement anyone took, and it is not attributed to Reclamation.
Surface area splits four ways too. Reclamation publishes 480 acres , its own 2018 survey measured 460.4 , and the hydrography polygon computes to about 432 . These are a design maximum, a measured surface and a cartographic polygon, so they are not really in conflict, but no single number covers all three.
The hinge of a river's pollution plan
This reservoir is the line that divides the Little Bear River's phosphorus plan in two, and the reach below it needs more than four times the cut the reach above it does.
The Little Bear River carries a total maximum daily load for total phosphorus and hydromodification, and its geography is defined by this reservoir .
| Segment | Length | Phosphorus cut required |
|---|---|---|
| East Fork to Hyrum Reservoir | 6.8 miles | 2.4 kg a day |
| Hyrum Reservoir to Cutler Reservoir | 28.1 miles | 13 kg a day above Cutler |
The impairment finding, verbatim: the segments "did not fully support aquatic life and cold water fishery designated uses due to high TP concentrations and hydromodification" . The standard is 0.05 milligrams a litre, and compliance means not exceeding it more than 25 percent of the time.
And there is a rare piece of good news here. Verbatim: "UDEQ removed the upper 6.8 miles of the Little Bear River from its 2004 303(d) list for TP" . The reach feeding this reservoir was cleaned up enough to come off the impaired list. What is not established is Hyrum Reservoir's own listing status. The plan describes the reservoir as a boundary and a reference point, not as an impaired water in its own right, and no source read says whether the reservoir itself is listed. This page says neither that it is nor that it is not.
Utah's water quality rule holds five Cache County waters. Hyrum reads 2A, 3A, 4: frequent primary contact, cold water game fish, agriculture .
| Water | Classes | |
|---|---|---|
| Hyrum Reservoir | 2A, 3A, 4 | Swimming tier |
| Porcupine Reservoir | 2B, 3A, 4 | A tier lower for recreation, twelve miles away |
| Newton Reservoir | Also in the table, no page here yet | |
What Hyrum does have is its own monitoring page, and it is cleaner than the assumption. The state runs recreational sampling here for both harmful algal blooms and E. coli, at the swim beach and day use area . The 25 June 2025 update reads, verbatim: "E. coli counts were measured below recreational thresholds and our monitoring team did not see any visible signs of a harmful algal bloom." The season closed on 1 November 2025.
This reservoir sits in the Bear River system, in hydrologic unit 16010203 , reaching the Bear by way of the Little Bear and Cutler Reservoir.
No fish consumption advisory names this water, and that was checked against both of Utah's two lists, which do not agree with each other. The health department carries twelve waters from a 2022 mercury analysis ; the environmental department carries roughly fifty water and species entries dated 4/23/18 . Hyrum is on neither. The only Cache County water on the longer list is Porcupine, for brown trout.
The shape in the header is traced from the Fathom print artwork, checked against the federal outline .
| Measure | Traced | Federal | Gap |
|---|---|---|---|
| Width against length | 0.8341 | 0.8602 | 3.04% |
| Share of its bounding box | 0.367 | 0.360 | 1.9% |
| Area, matched on length | 426.0 acres | 431.5 acres | 1.3% under |
| Area, matched on width | 453.1 acres | 431.5 acres | 5.0% over |
Long axis 1.48 miles, width 1.27. This is a broad, blunt reservoir, and the shape is the drowned lower end of a valley rather than a canyon.
Storage comes from soil conservation service station 10107000:UT:BOR, daily since 1 October 1970 . It serves daily, semimonthly and monthly, and daily is the only one flagged not derived, so it is the only one that is observed rather than computed. That is what the card reads.
And there is a live flow card, which the last four pages in this series could not manage. USGS 10105900, Little Bear River at Paradise, draining 182 square miles, continuous since October 1992 and reporting today .
The water survey also once measured the reservoir itself, at a site sharing the storage station's number. That record ran from 31 October 1965 to 30 September 1980 and stopped .
The percentage card needs a stated denominator and this page states it. It divides by 18,221 acre feet, the 2018 surveyed capacity . Dividing by the published design figure of 18,685 instead would move the number by about seven tenths of a percentage point. Elevation is worth the same caution: Reclamation gives a crest of 4,680 feet and a reference elevation of 4,672.5, the hydrography dataset carries 4,664 and the gauge station sits at 4,660. Those are four different surfaces, not four answers to one question.
Where everything is
Eight places, two of which are separate structures on the same dam record, and two of which are gauges that stopped decades ago.
Hyrum State Park sits on the north shore . The reservoir underneath it is a 1935 Public Works Administration irrigation asset that still delivers to three canals at three elevations, one of them needing a pumping plant .
One agency source could not be read and the failure is worth naming. The state parks fee sub page for this park served content for a golf course in a different part of Utah entirely. That is the second time in three builds that the state parks sub page routing has done this, so no fee figure from that path appears here.
Hyrum Reservoir is not open to underwater spearfishing. That is double sourced and safe: it is absent from the rule and absent from the guidebook's page 19 list .
The guidebook page cites the rule by number as its authority. The guidebook is the agency's own current publication; the forty two water list reaches this page through a law school library reproduction, because Utah's rules site returns errors for the rule text. Either the reproduction is of a superseded version, or the guidebook prints a curated subset. This page picks neither. None of it changes the answer for Hyrum, which is on neither.
The only Cache County water open to spearfishing is Porcupine Reservoir, and it appears on both lists . Twelve miles away, and the answer to the only question a diver in this valley is going to ask.
One statewide allowance does apply here and it needs reading carefully. The guidebook permits underwater spearfishing for common carp and Utah chub at any water open to fishing . It does not name Utah sucker, which is the species that actually dominates this reservoir. This page does not claim the allowance covers it.
No SCUBA or diving rule specific to this water was found in any source. The zoned waters rule has eighteen sections and none of them is Hyrum . That is an absence, not a permission and not a prohibition.
The division measured it, and wrote down what it found
Six species, four of them near zero, one of them 91 percent of the catch, and a management note about introducing something new to deal with it.
Utah sucker
The story of this reservoir. In the division's 2023 survey it was 91.0 percent of the gillnet catch by number and 94.6 percent by weight . 97 percent of those caught were of quality length or better and 17 percent were trophy length, at a mean relative weight of 99.1, essentially the reference standard. These fish are not struggling.
91% of the gillnet catchLargemouth bass
The counterweight, and the one genuinely good angling finding in the report. Mean relative weight 107.3, above standard, and multiple fish in the preferred length category "observed for the first time" . The catch rate is not solid: 12.0 fish an hour with a standard error of 12.0, from ten minutes of shocking.
Condition above standardRainbow trout
Stocked to quota and not surviving. The division writes "Rainbow Trout do not appear to be well-supported in the reservoir" . Found only in the stock length category, mean relative weight 79.8 against a standard of 100, and a length distribution statistically shifted since 2012 at P = 0.030. Drawn thin for that reason.
Not well supportedBrown trout
Caught, and barely. The size metrics in the report read 67, 67, 67 across three categories, which is what two fish out of three looks like, and the division says plainly that "sample sizes were low" . This page prints no brown trout size figures, because there is nothing behind them.
Too few to measureYellow perch
Once one of the three species that defined this water. In 2023 its relative abundance and biomass had decreased to at or near zero . It is still legal to use dead yellow perch as bait here, which is one of only eighteen waters in Utah where that is true .
Near zeroBluegill
Targeted in the survey, caught along the shoreline, and part of the same collapse: its abundance and biomass are in the group the division reports as decreased to at or near zero . Mean length 3.9 inches. No relative weight was computed for it.
Near zeroEvery page in this series tries to read the wildlife division's own fishery report for the water. For four lakes running it did not exist, or could not be found. Here it does, it can, and it was read in full .
Eight overnight gillnets on 18 May 2023 and a shoreline electrofishing run on 9 May. The sentence that defines this page, verbatim:
"The fish community has shifted over time from being dominated largely by Brown Trout, Rainbow Trout, and Yellow Perch to a less diverse fish community with" largemouth bass and Utah sucker having important roles .
The upper bound of that range is one hundred percent, which means at least one of those four species registered a biomass of zero. The report does not say which one.
The division flags its own caveat and this page carries it: sampling was to be repeated "to ensure the high-water year observed in 2023 did not skew results" . The 2024 follow up could not be found, and neither could 2022. The 2023 report benchmarks against gillnet sampling in 2012 and electrofishing in 2007, so a survey series exists going back at least eighteen years and this is the one instalment that could be read.
The report ends with two numbered management actions. The first, verbatim and complete :
"Sampling will be conducted again in 2024 to ensure the high-water year observed in 2023 did not skew results. These two years of data will be used to guide aggressive management actions (e.g., novel species introduction) in the future with the primary objective of controlling the Utah Sucker population."
The second action is candour of a different kind: "Evaluate stocking efforts. Rainbow Trout do not appear to be well-supported in the reservoir. The increase in littoral, warmwater species suggests that the thermal and trophic dynamics may have shifted within the reservoir."
Read that against the stocking line and it lands harder. The same report states "Stocking quotas are being met and maintained" . The division records rainbow trout going in on schedule, and the fish it catches are thin, small, and statistically shifted downward since 2012. The fish are going in and they are not growing. The stocking database shows 5,580 rainbow trout in February 2026 and 648 more in March .
"Thermal and trophic dynamics may have shifted" is the division raising, in a fishery document, the possibility that the reservoir itself has changed. It is speculative in the source and it stays speculative here. But it is the sentence that ties this section to the phosphorus plan above it.
There is no Hyrum Reservoir entry in the fishing guidebook. The word Hyrum appears exactly once in the whole document, and it is not a water heading . The statewide rules govern this reservoir entirely.
That single appearance is on the bait list, verbatim:
"Dead yellow perch may be used as bait only in these waters: Big Sand Wash, Deer Creek, Echo, Fish Lake, Gunnison, Hyrum, Johnson, Jordanelle, Mantua, Mill Meadow, Newton, Pineview, Red Fleet, Rockport, Starvation, Utah Lake, Willard Bay and Yuba reservoirs."
The entry immediately before Hyrum's in the same rule is Bear Lake's, for dead Bonneville cisco, which is the only other water specific bait exception in the guidebook.
The list was checked four ways, including a separately issued question phrased so that "no" was the easy answer, and it survives all four in the same word order. Blue Ribbon status is unresolved: the division states a count of designated waters and does not print the list.
What to watch for
Three drownings in nine years, in two distinct places, and only one of the three supports the sentence people write about it.
At least three separate drowning deaths at Hyrum Reservoir are documented in press between 2014 and 2023. They did not happen in the same place, and telling them apart is the most useful thing this section can do.
| Date | Where | How located |
|---|---|---|
| 9 July 2014 | Southwest section of the reservoir, swimming without a life jacket about twenty feet out | Not stated |
| 25 May 2018 | The Big Toe, east side of the dam, after jumping from the cliff | Bystanders saw him go under; the recovery method is not stated |
| 25 to 26 June 2023 | Under the day use beach dock at the state park, about eight feet down | Divers, stated explicitly by two outlets |
The 2014 search had a dive team AND three vessels with side scan sonar in the water, and no account says which found him . So this page does not write "found by sonar" and does not write "found by divers" for that one. It says what the record says: both were searching, and the reporting does not distinguish them.
The 2018 death was at the dam, not the beach. Coverage describes the east side of the dam as a restricted area where roughly forty teenagers had gathered to jump from a feature known as the Big Toe . That is not the state park swimming beach, and conflating them is both inaccurate and unfair to the park.
The 2023 death happened under the Hyrum Day Beach Dock at Hyrum State Park, on the authority of the outlet that names the dock .
The dam, the dike, the reservoir, the state park and the town all carry the same name, and a page assembled from headlines would place a child's death at the wrong end of the reservoir. This page places it at the beach, and says why.
What was not found. No boating fatality, no capsizing, no ice incident, no vehicle in the water, and no incident of any kind on the Little Bear River above or below the reservoir. Those are searches that returned nothing, not searches that were skipped. The publishable form is "no incident found in searchable press", never "none has occurred." The local paper of record for Cache Valley rate limited every attempt to read it, and it would very likely be the most detailed account of all three.
Nobody publishes a depth for this reservoir. The nearest thing to a public statement about how deep the swimming water gets comes from the 2014 drowning coverage, which describes the search area as ranging from fifteen to thirty feet deep .
The state does sample this water for both algae and bacteria, at the swim beach and the day use area, and the last published result was clean . Monitoring runs roughly June to November. That is a real, current, agency programme on the exact stretch of shoreline people swim from.
Two teams searched in 2014. Nine years later, two outlets finally named who found him.
Fathom Restoration is a Utah 501(c)(3) that runs volunteer dive cleanups and is built to pull what does not belong out of Utah water, statewide.
Donate to Protect HyrumEvery figure on this page is quoted from the source named beside it.
Sources
How these were checked
Numbered sources are agencies. Lettered sources are everything else: three reproductions of Utah rules that the state's own rules site returns errors for, and four news accounts of three drownings. Source 11 is the reason this page exists in this shape. It is the wildlife division's own 2023 fishery survey of this reservoir, and it is the first one in five lakes that could actually be read, which is why the fishing section on this page quotes measurements rather than impressions. Where sources disagree, all of them are printed: that happens over the reservoir's capacity, its surface area, its elevation, which waters are open to spearfishing, and who found a body in 2014. One lead this page started with did not survive: the belief that Hyrum is on the state's harmful algal bloom monitoring list. It is not, and the list turned out to be a 2018 archive.Hyrum Project. Stores and diverts water from the Little Bear River to furnish supplemental water supplies to 6,800 acres, authorised under the National Industrial Recovery Act of 1933, funded by the Public Works Administration in August 1933, built March 1934 to August 1935, first storage 1 April 1935, first delivery July 1935, presidential approval November 1935, dam contractor J. A. Terteling and Sons on a bid of 337,221 dollars
Hyrum Dam data. Structural height 116 feet, hydraulic height 82, crest 540 feet at elevation 4,680, capacity 18,685 acre feet, surface area 480 acres, spillway 6,000 cubic feet a second at 4,672.0 and outlet works 300 at 4,666.0, and a coordinate published to fifteen decimal places
Hyrum Reservoir bathymetric survey, technical report ENV-2019-067, by Robert C. Hilldale, August 2019, surveyed 29 to 30 October 2018 with the water about twenty feet down. Capacity 18,221 acre feet at elevation 4,672.5, against 17,746 in 2006 and 18,685 in 1946, and a surveyed surface area of 460.4 acres
National Inventory of Dams, records UT10123 and UT10123S001. Two structures under one identifier: Hyrum Dam at 116 feet with a 540 foot crest, and Hyrum Dike at 18 feet with an 850 foot crest. The reservoir name appears only in the other names field on both
National Hydrography Dataset, Hyrum Reservoir, GNIS 01427299, reach code 16010203000454, published at 1.748 square kilometres with an elevation field of 4,664 feet
Watershed boundary dataset. Hyrum Reservoir sits in hydrologic unit 16010203, the Bear River system by way of the Little Bear
Hyrum Reservoir storage, station 10107000:UT:BOR, at 4,660 feet. Daily reservoir contents since 1 October 1970, and the only duration here flagged not derived
Little Bear River at Paradise, site 10105900, draining 182 square miles. Continuous record since 1 October 1992 and live today
Little Bear River near Hyrum, site 10107500, below the dam at 4,520 feet. Daily discharge from 1 October 1942 to 1 March 1974 and nothing since
Hyrum Reservoir, lake site 10107000. Reservoir contents from 31 October 1965 to 30 September 1980 and nothing since
Hyrum Reservoir fishery monitoring report, sampled 9 and 18 May 2023, by Taylor R. Stewart. Eight overnight gillnets and a shoreline electrofishing run. Utah sucker were 91.0 percent of the gillnet catch by number and 94.6 percent by weight, rainbow trout do not appear to be well supported in the reservoir, and the division may pursue aggressive management actions including novel species introduction to control the sucker population
Fish stocking records. Rainbow trout into Hyrum Reservoir in February and March 2026
2026 Utah Fishing Guidebook. Hyrum appears exactly once in the whole document, on the dead yellow perch bait list, and there is no water specific entry for it. Page 19 lists the waters open to spearfishing and Hyrum is not among them
Upper Little Bear River total maximum daily load, June 2008. Two segments defined by Hyrum Reservoir: 6.8 miles above it and 28.1 miles below. Total phosphorus standard 0.05 milligrams a litre, load reductions of 2.4 kilograms a day above Hyrum and 13 above Cutler, and the upper 6.8 miles were removed from the 2004 impaired waters list
Hyrum Reservoir recreational water quality monitoring. E. coli and harmful algal bloom monitoring at the swim beach and day use area, a clean sample on 25 June 2025, and the season closed on 1 November 2025
Harmful algal blooms. Twenty five waters were monitored in the 2018 season and Hyrum Reservoir is not one of them
Utah fish consumption advisories. Roughly fifty water and species entries, dated 4/23/18. No Hyrum entry, and the only Cache County water on it is Porcupine Reservoir
Game and fish advisories. Twelve Utah waters from a 2022 mercury analysis, and no Hyrum entry
Hyrum State Park. Fees, hours, camping and the description of the reservoir
Point forecast for the reservoir. Forecast office Salt Lake City
Utah Administrative Code R317-2-13, classification of waters. The Cache County table holds five waters: Hyrum, Newton, Porcupine, Pelican Pond and Tony Grove. Hyrum reads 2A, 3A, 4 and Porcupine reads 2B
Utah Administrative Code R657-13-9, underwater spearfishing. Forty two waters, running a to pp, with Porcupine at entry y as the only Cache County water and no Hyrum entry
Utah Administrative Code R650-205, the zoned waters rule. Eighteen sections and no Hyrum section
Body of missing teen recovered in Hyrum Reservoir, July 2014. A dive team and three vessels with side scan sonar searched; the account does not say which found him
Body of teen who drowned at Hyrum Reservoir recovered, May 2018. At the Big Toe on the east side of the dam, described as a restricted area, with about forty teenagers present
Body of 14 year old boy recovered from Hyrum Reservoir, June 2023. Divers located and recovered him about eight feet under the day use beach dock, roughly nineteen and a half hours after he was last seen
Cache County sheriff searching for a missing boy, June 2023. The dive team located the body, and the article's own web address places the search at Hyrum Dam when the beach is not at the dam
The flow card is an inflow gauge, not a release
The flow number on this page is USGS 10105900, Little Bear River at Paradise . Paradise is upstream, about five and a half kilometres from the dam. That gauge measures water going into this reservoir.
Nothing measures what comes out. USGS 10107500, below the dam, published daily discharge from 1 October 1942 and stopped on 1 March 1974 . Nothing continuous has replaced it in fifty two years.
The percentage card divides by 18,221 acre feet, which is what Reclamation's 2018 bathymetric survey measured at elevation 4,672.5 . Reclamation and the dam inventory both still publish 18,685, which is the original design figure . Using that denominator instead would move the percentage by roughly seven tenths of a point. The 2006 survey measured 17,746, which is less than either, and a reservoir cannot gain capacity between two surveys. Reclamation does not explain it and neither does this page.
The storage reading comes from station 10107000:UT:BOR , daily since 1 October 1970. It serves daily, semimonthly and monthly, and only the daily series is flagged as observed rather than computed, so that is the one the card reads. The record has gaps: do not assume yesterday has a value.