Prewitt Reservoir
Washington County, Colorado2,329 acresView mapDirections
Colorado WQCD publishes the water-quality measurements for Prewitt Reservoir. Here is what has been measured.
- 82 ft max depth
- Public access
- Limited data
Prewitt Reservoir in Washington County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 1.8 ft visibility. Phosphorus: 87 µg/L. Chlorophyll-a (algae): 31.5 µg/L. Surface area: 2329 acres.
Prewitt Reservoir is a 2,329-acre lake in Washington County, Colorado with an estimated average depth of about 82 feet. Limited fish-species data available. Public access is available.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2023-11-06. Methodology: how these readings are compared.
What Prewitt Reservoir is good for
From access and monitoring records, not editorial picks.
- Big water2,329 acres
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Prewitt Reservoir is safe to swim in today is a call for the Water Quality Control Division of the Colorado Department of Public Health and Environment and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Prewitt Reservoir
These are the measurements Colorado WQCD publishes for Prewitt Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.8 ft of visibility. Phosphorus 87 µg/L. Chlorophyll-a 31.5 µg/L. TSI 67.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.8ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 87µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 31.5µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 67 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Prewitt Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~82 ft est.
Surface area
2,329 acres
Public access
Yes
Listed by Colorado WQCD
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Colorado has not published bathymetry for Prewitt Reservoir.
Lake Size & Watershed
Watershed (drainage) area
28 sq mi
HydroLAKES / HydroSHEDS
Shoreline
9.1 mi
HydroLAKES / HydroSHEDS
Elevation
4,088 ft
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.
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Stays near Prewitt Reservoir
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Fishing Prewitt Reservoir
Reservoir Info (USACE NID)
Prewitt Reservoir is a man-made reservoir impounded by the Prewitt (completed 1912), built primarily for irrigation on the South Platte River-Os; earth-type dam, 43 ft tall and 15,400 ft long.
- Surface area
- 2,329 ac
- Normal storage
- 28,840 ac-ft
- Max storage
- 51,387 ac-ft
- Drainage area
- 105 sq mi
- Hazard class
- High
- Owner
- LOGAN IRRIGATION DISTRICT (YAHN, JIM)
Source: USACE National Inventory of Dams, NID ID CO00385 · Operator website
Nearby Lakes in Washington County
Frequently asked questions about Prewitt Reservoir
Where is Prewitt Reservoir?
- Prewitt Reservoir is a lake in Washington County, Colorado. Its water-quality measurements are published by Colorado WQCD and shown on this page as reported.
What is the water quality of Prewitt Reservoir?
- Prewitt Reservoir in Washington County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 1.8 ft visibility. Phosphorus: 87 µg/L. Chlorophyll-a (algae): 31.5 µg/L. Surface area: 2329 acres.
Is Prewitt Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is Prewitt Reservoir?
- No published bathymetric survey covers Prewitt Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 82 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 2329 acres.
Can I fish at Prewitt Reservoir?
- Public access to Prewitt Reservoir is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Colorado's fish and wildlife agency, so check its current regulations before you go.
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Where this data comes from
7 measurements from 2 monitoring stations, 2021–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Colorado Dept. of Public Health & Environment-WQCD
21COL001_WQX7 samples · 2021–2023
Analytical methods
- Secchi disk depth measurement
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Nitrogen in Water by Pyrolysis Detection
Monitoring station identifiers (2)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)