Upper Stillwater Reservoir
Duchesne County, Utah329 acresView mapDirections
Utah DWQ publishes the water-quality measurements for Upper Stillwater Reservoir. Here is what has been measured.
- Mesotrophic
- Limited data
Upper Stillwater Reservoir in Duchesne County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 8.7 ft visibility. Phosphorus: 11.1 µg/L. Chlorophyll-a (algae): 2.8 µg/L. Surface area: 329 acres.
Upper Stillwater Reservoir is a 329-acre mesotrophic lake in Duchesne County, Utah. Overall water quality is improving over recent sampling years. Compared to the 8 other monitored lakes in Duchesne County, Upper Stillwater Reservoir ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2024-07-29. Methodology: how these readings are compared.
Upper Stillwater Reservoir covers about 330 acres in Duchesne County. For a place on the water, look through cabin and lake-house rentals near Upper Stillwater Reservoir on Vrbo. For a hotel or motel room, Booking.com and Expedia both search around the lake.
What Upper Stillwater Reservoir is good for
From access and monitoring records, not editorial picks.
- Camping1 public campground nearby
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Upper Stillwater Reservoir is safe to swim in today is a call for the Utah Division of Water Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Upper Stillwater Reservoir
These are the measurements Utah DWQ publishes for Upper Stillwater Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 8.7 ft. Phosphorus 11.1 µg/L. Chlorophyll-a 2.8 µg/L. TSI 42.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 8.7ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 11.1µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.8µg/L | Fair GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 42 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Upper Stillwater Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
329 acres
No bathymetric survey has been published for Upper Stillwater Reservoir, so its depth is not documented here.
Recreation & Access
Public campgrounds near Upper Stillwater Reservoir
- Upper Stillwater0.1 kmReserve
Nearest public campgrounds in the USGS National Map inventory, within about 3 miles. An empty list means USGS records no campground that close, which is not the same as camping being unavailable. Where the source gives an official reservation link, it is used; the cabin and hotel search does not cover campsites. More camping lakes
Stays via Stay22
Stays near Upper Stillwater Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Upper Stillwater Reservoir in Duchesne County, Utah — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Upper Stillwater Reservoir
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Fishing Upper Stillwater Reservoir
Water quality readings over time
2 seasons of samples on record (2023–2024). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Improving2 years
Phosphorus
Improving-0.8 µg/L/yr2 years
Chlorophyll-a
Improving-5 µg/L/yr2 years
Reservoir Info (USACE NID)
Upper Stillwater Reservoir is a man-made reservoir impounded by the Upper Stillwater Dam (completed 1987), built primarily for irrigation on the Rock Creek; concrete-type dam, 292 ft tall and 2,660 ft long.
- Surface area
- 329 ac
- Normal storage
- 33,123 ac-ft
- Max storage
- 35,253 ac-ft
- Drainage area
- 98.9 sq mi
- Hazard class
- High
- Owner
- DEPARTMENT OF THE INTERIOR
All listed purposes: Irrigation;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID UT00608 · Operator website
Nearby Lakes in Duchesne County
Frequently asked questions about Upper Stillwater Reservoir
Where is Upper Stillwater Reservoir?
- Upper Stillwater Reservoir is a lake in Duchesne County, Utah. Its water-quality measurements are published by Utah DWQ and shown on this page as reported.
What is the water quality of Upper Stillwater Reservoir?
- Upper Stillwater Reservoir in Duchesne County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 8.7 ft visibility. Phosphorus: 11.1 µg/L. Chlorophyll-a (algae): 2.8 µg/L. Surface area: 329 acres.
Is Upper Stillwater Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Are there campgrounds on Upper Stillwater Reservoir?
- Upper Stillwater Reservoir has 1 public campground from USGS The National Map within 5 km, including Upper Stillwater. This is a location join, not a booking. Cabins and hotels are listed separately; campsite reservations use the official link when the source provides one.
Explore Upper Stillwater Reservoir across LakeQuality
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Mesotrophic Lakes in Utah
Where this data comes from
15 measurements from 1 monitoring station, 2017–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX15 samples · 2017–2024
Analytical methods
- Field Measurements
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Public campgrounds from USGS The National Map Structures, within about 3 miles