Big Sand Wash Reservoir
Duchesne County, UtahView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Mesotrophic
- Impaired · Impaired biota (cause unknown)
- #2 of 9 in the county
- 22 ft max depth
- Limited data
Big Sand Wash Reservoir in Duchesne County, Utah has a water quality grade of A (Excellent). Water clarity: 10.7 ft visibility. Phosphorus: 11.7 µg/L. Chlorophyll-a (algae): 2.3 µg/L.
- Clarity
- 10.7 ft
- Max depth
- ~22 ft est.
- Type
- Mesotrophic
- Phosphorus
- 11.7 µg/L
- Chlorophyll-a
- 2.3 µg/L
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Watch Big Sand Wash Reservoir’s letter
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Big Sand Wash Reservoir is a mesotrophic lake in Duchesne County, Utah with an estimated average depth of about 22 feet. Water quality is graded A based on 2 sampling years through 2023. Public access is available with 1 public boat landing. Compared to the 8 other monitored lakes in Duchesne County, Big Sand Wash Reservoir ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2023-08-22. Grade methodology: LakeQuality methodology.
What Big Sand Wash Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water10.7 ft of visibility
- Boat launch1 documented ramp
Swimming Safety
Grade onlyLimited data
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. Big Sand Wash Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), metals (other than mercury), oxygen depletion (low DO), salinity / chlorides, temperature. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Good clarity, visible to about 10.7 ft. Phosphorus 11.7 µg/L. Chlorophyll-a 2.3 µg/L. TSI 41. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10.7 ft | Not graded |
| Phosphorus | 11.7 µg/L | Good |
| Chlorophyll-a (Algae) | 2.3 µg/L | Good |
| Trophic State Index (TSI) | 41 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~22 ft est. |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Utah has not published bathymetry for Big Sand Wash Reservoir.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Big Sand State ParkSemi-private
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Big Sand Wash Reservoir
Reservoir Info (USACE NID)
Big Sand Wash Reservoir is a man-made reservoir impounded by the Big Sand Wash West (completed 2006), built primarily for irrigation on the Big Sand Wash; earth-type dam, 55 ft tall and 2,950 ft long.
- Normal storage
- 18,800 ac-ft
- Max storage
- 19,600 ac-ft
- Drainage area
- 26.64 sq mi
- Hazard class
- High
- Owner
- MOON LAKE WATER USERS
Source: USACE National Inventory of Dams, NID ID UT53328 · Operator website
EPA Impairment Status
Big Sand Wash Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit UT14060003-008_00 · Official waterbody report · Matched by proximity (2.58 km)
County Ranking
Ranked #2 of 9 lakes in Duchesne County
Nearby Lakes in Duchesne County
Frequently asked questions about Big Sand Wash Reservoir
Where is Big Sand Wash Reservoir?
- Big Sand Wash Reservoir is a lake in Duchesne County, Utah. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Big Sand Wash Reservoir?
- Big Sand Wash Reservoir in Duchesne County, Utah has a water quality grade of A (Excellent). Water clarity: 10.7 ft visibility. Phosphorus: 11.7 µg/L. Chlorophyll-a (algae): 2.3 µg/L.
Is Big Sand Wash Reservoir safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Big Sand Wash Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), metals (other than mercury), oxygen depletion (low DO), salinity / chlorides, temperature. Check local advisories before you swim.
How deep is Big Sand Wash Reservoir?
- No published bathymetric survey covers Big Sand Wash Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 22 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Big Sand Wash Reservoir?
- Big Sand Wash Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Big Sand State Park.
Explore Big Sand Wash Reservoir across LakeQuality
More Utah Lake Rankings
Other Grade A Lakes in Utah
Mesotrophic Lakes in Utah
Where this data comes from
16 measurements from 1 monitoring station, 2017–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX16 samples · 2017–2023
Analytical methods
- Field Measurements
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory