Deweese Reservoir
Custer County, Colorado295 acresView mapDirections
Colorado WQCD publishes the water-quality measurements for Deweese Reservoir. Here is what has been measured.
- Eutrophic
- Impaired · Metals (other than mercury)
- 21 ft max depth
- Public access
Deweese Reservoir in Custer County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 5.2 ft visibility. Phosphorus: 41.5 µg/L. Chlorophyll-a (algae): 13.5 µg/L. Surface area: 295 acres.
Deweese Reservoir is a 295-acre productive, nutrient-rich eutrophic lake in Custer County, Colorado with an estimated average depth of about 21 feet. Phosphorus level is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2025-10-01. Methodology: how these readings are compared.
What Deweese Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming conditions
Readings onlyElevated nutrients
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. Deweese Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury), nutrients (phosphorus, nitrogen), oxygen depletion (low DO). Check local advisories before you swim.
Whether Deweese 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 Deweese Reservoir
These are the measurements Colorado WQCD publishes for Deweese Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.2 ft. Phosphorus 41.5 µg/L. Chlorophyll-a 13.5 µg/L. TSI 56.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.2ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 41.5µg/L | Fair GoodFairPoor |
| Chlorophyll-a (algae) | 13.5µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 56 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Deweese Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~21 ft est.
Surface area
295 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 Deweese Reservoir.
Lake Size & Watershed
Watershed (drainage) area
349 sq mi
HydroLAKES / HydroSHEDS
Shoreline
4.3 mi
HydroLAKES / HydroSHEDS
Elevation
7,684 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.
Recreation & Access
- DeWeese Reservoir State Wildlife AreaPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Deweese Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Deweese Reservoir in Custer County, Colorado — 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Deweese Reservoir are listed below.
Top-rated places to stay near Deweese Reservoir
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Planning a trip? Cabins and lodging at Deweese Reservoir → · more Colorado lake trips
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Fishing Deweese Reservoir
Water quality readings over time
3 seasons of samples on record (2020–2025). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Stable3 years
Phosphorus
Improving-15.25 µg/L/yr2 years
Chlorophyll-a
Worsening+0.44 µg/L/yr3 years
Reservoir Info (USACE NID)
Deweese Reservoir is a man-made reservoir impounded by the Deweese (completed 1903), built primarily for irrigation on the Grape Creek; arch-type dam, 63 ft tall and 386 ft long.
- Surface area
- 295 ac
- Normal storage
- 4,338 ac-ft
- Max storage
- 4,441 ac-ft
- Drainage area
- 370 sq mi
- Hazard class
- High
- Owner
- DE WEESE DYE DITCH & RES. CO. (ARLIN BOLKEMA, PRES
All listed purposes: Irrigation;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID CO02068 · Operator website
EPA Impairment Status
Deweese Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Drinking water, Aquatic life.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit COARUA35_A · Official waterbody report
Nearby Lakes in Custer County
Frequently asked questions about Deweese Reservoir
Where is Deweese Reservoir?
- Deweese Reservoir is a lake in Custer County, Colorado. Its water-quality measurements are published by Colorado WQCD and shown on this page as reported.
What is the water quality of Deweese Reservoir?
- Deweese Reservoir in Custer County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 5.2 ft visibility. Phosphorus: 41.5 µg/L. Chlorophyll-a (algae): 13.5 µg/L. Surface area: 295 acres.
Is Deweese Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Deweese Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury), nutrients (phosphorus, nitrogen), oxygen depletion (low DO). Check local advisories before you swim.
How deep is Deweese Reservoir?
- No published bathymetric survey covers Deweese Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 21 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 295 acres.
Are there boat ramps on Deweese Reservoir?
- Deweese Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include DeWeese Reservoir State Wildlife Area. Public access is listed as yes.
Can I fish at Deweese Reservoir?
- Deweese Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. 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.
Explore Deweese Reservoir across LakeQuality
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Planning a trip around Great Sand Dunes?
Deweese Reservoir is about 29 miles from Great Sand Dunes National Park & Preserve. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Great Sand Dunes →More lakes in Colorado
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Where this data comes from
78 measurements from 5 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Colorado Dept. of Public Health & Environment-WQCD
21COL001_WQX78 samples · 2020–2025
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 (5)
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
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