Hyrum Reservoir
Cache County, Utah480 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Mesotrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #2 of 9 in the county
- Public access
Hyrum Reservoir in Cache County, Utah has a water quality grade of A (Excellent). Water clarity: 6.9 ft visibility. Phosphorus: 17.9 µg/L. Chlorophyll-a (algae): 2.2 µg/L. Surface area: 480 acres.
- Clarity
- 6.9 ft
- Area
- 480 acres
- Type
- Mesotrophic
- Phosphorus
- 17.9 µg/L
- Chlorophyll-a
- 2.2 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Watch Hyrum Reservoir’s letter
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Hyrum Reservoir is a 480-acre mesotrophic lake in Cache County, Utah. Water quality is graded A based on 2 sampling years through 2021. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 8 other monitored lakes in Cache County, Hyrum Reservoir ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2021-09-15. Grade methodology: LakeQuality methodology.
What Hyrum Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming Safety
Grade onlyLow algae
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The A is nutrients and algae, not a swimming clearance. Hyrum Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Moderate clarity, visible to about 6.9 ft. Phosphorus 17.9 µg/L. Chlorophyll-a 2.2 µg/L. TSI 44. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.9 ft | Not graded |
| Phosphorus | 17.9 µg/L | Good |
| Chlorophyll-a (Algae) | 2.2 µg/L | Good |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 480 acres |
| Public Access | Yes |
No bathymetric survey has been published for Hyrum Reservoir, so its depth is not documented here.
Recreation & Access
- Hyrum State ParkPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Hyrum Reservoir
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.27 m/yr | 5 |
| Phosphorus | ↓ Declining | +1.4 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -0.1 µg/L/yr | 3 |
Reservoir Info (USACE NID)
Hyrum Reservoir is a man-made reservoir impounded by the Hyrum Dike (completed 1935), built primarily for irrigation on the Little Bear River; earth-type dam, 18 ft tall and 850 ft long.
- Surface area
- 480 ac
- Normal storage
- 18,685 ac-ft
- Max storage
- 18,685 ac-ft
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Irrigation;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID UT10123 · Operator website
EPA Impairment Status
Hyrum Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit UT-L-16010203-005_00 · Official waterbody report
County Ranking
Ranked #2 of 9 lakes in Cache County
Nearby Lakes in Cache County
Frequently asked questions about Hyrum Reservoir
Where is Hyrum Reservoir?
- Hyrum Reservoir is a lake in Cache County, Utah. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Hyrum Reservoir?
- Hyrum Reservoir in Cache County, Utah has a water quality grade of A (Excellent). Water clarity: 6.9 ft visibility. Phosphorus: 17.9 µg/L. Chlorophyll-a (algae): 2.2 µg/L. Surface area: 480 acres.
Is Hyrum Reservoir safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Hyrum Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Are there boat ramps on Hyrum Reservoir?
- Hyrum Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Hyrum State Park. Public access is listed as yes.
Explore Hyrum Reservoir across LakeQuality
11.7 mi away · recorded at 129°F
Species activity outlook by water temperature and season
Where to stay at Utah's top lakes, each with its grade
Moderate nutrients, good water quality
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Where this data comes from
194 measurements from 2 monitoring stations, 2015–2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX194 samples · 2015–2021
Analytical methods
- Field Measurements
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (2)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Named boat-access points from the USGS National Boat Ramps inventory