Lake Nighthorse
La Plata County, Colorado1,548 acresView mapDirections
Colorado WQCD publishes the water-quality measurements for Lake Nighthorse. Here is what has been measured.
- Oligotrophic
- Impaired · Metals (other than mercury)
- Limited data
Lake Nighthorse in La Plata County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 18.7 ft visibility. Phosphorus: 45 µg/L. Chlorophyll-a (algae): 0.7 µg/L. Surface area: 1548 acres.
Lake Nighthorse is a 1,548-acre cold, clear oligotrophic lake in La Plata County, Colorado. Overall water quality is improving over recent sampling years. Compared to the 1 other monitored lakes in La Plata County, Lake Nighthorse ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2023-09-13. Methodology: how these readings are compared.
What Lake Nighthorse is good for
From access and monitoring records, not editorial picks.
- Clear water18.7 ft of visibility
- Big water1,548 acres
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. Lake Nighthorse is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury). Check local advisories before you swim.
Whether Lake Nighthorse 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 Lake Nighthorse
These are the measurements Colorado WQCD publishes for Lake Nighthorse, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 18.7 ft down. Phosphorus 45 µg/L. Chlorophyll-a 0.7 µg/L. TSI 40.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 18.7ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 45µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 0.7µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 40 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Lake Nighthorse
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
1,548 acres
No bathymetric survey has been published for Lake Nighthorse, so its depth is not documented here.
Stays via Stay22
Stays near Lake Nighthorse
Compare lakeside cabins, hotels, and vacation rentals near Lake Nighthorse in La Plata 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.
Top-rated places to stay near Lake Nighthorse
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Fishing Lake Nighthorse
Water quality readings over time
2 seasons of samples on record (2021–2023). Calling a direction takes at least 4 years of the same measurement.
Chlorophyll-a
Improving-1.4 µg/L/yr2 years
Reservoir Info (USACE NID)
Lake Nighthorse is a man-made reservoir impounded by the Ridges Basin Dam (completed 2008), built primarily for water supply on the Basin Creek; earth-type dam, 273 ft tall and 1,600 ft long.
- Surface area
- 1,548 ac
- Normal storage
- 121,070 ac-ft
- Max storage
- 139,809 ac-ft
- Drainage area
- 13.88 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
Source: USACE National Inventory of Dams, NID ID CO02952 · Operator website
EPA Impairment Status
Lake Nighthorse 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.
Source: EPA ATTAINS assessment unit COSJAF22_A · Official waterbody report
Nearby Lakes in La Plata County
Frequently asked questions about Lake Nighthorse
Where is Lake Nighthorse?
- Lake Nighthorse is a lake in La Plata County, Colorado. Its water-quality measurements are published by Colorado WQCD and shown on this page as reported.
What is the water quality of Lake Nighthorse?
- Lake Nighthorse in La Plata County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 18.7 ft visibility. Phosphorus: 45 µg/L. Chlorophyll-a (algae): 0.7 µg/L. Surface area: 1548 acres.
Is Lake Nighthorse safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Lake Nighthorse is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury). Check local advisories before you swim.
Explore Lake Nighthorse across LakeQuality
3 thermal springs within 16.9 mi, nearest Trimble Hot Spr, Stratten Warm Spr
Species activity outlook by water temperature and season
Where to stay at Colorado's top lakes, each with its readings
Colorado's cleanest lakes, ranked on agency measurements
Planning a trip around Mesa Verde?
Lake Nighthorse is about 31 miles from Mesa Verde National Park. 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 Mesa Verde →More lakes in Colorado
Other Lakes in Colorado
Oligotrophic Lakes in Colorado
Where this data comes from
29 measurements from 4 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_WQX29 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 (4)
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