Prospect Lake
Weld County, Colorado398 acresView mapDirections
Colorado WQCD publishes the water-quality measurements for Prospect Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · pH / acidity
- 18 ft max depth
Prospect Lake in Weld County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Phosphorus: 300 µg/L. Chlorophyll-a (algae): 42.5 µg/L. Surface area: 398 acres.
Prospect Lake is a 398-acre highly nutrient-loaded hypereutrophic lake in Weld County, Colorado with an estimated average depth of about 18 feet. Overall water quality is declining over recent sampling years. Compared to the 4 other monitored lakes in Weld County, Prospect Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2024-09-25. Methodology: how these readings are compared.
Swimming conditions
Readings onlyAlgae risk
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. Prospect Lake is listed impaired under Clean Water Act §303(d) (IR 5) for pH / acidity. Check local advisories before you swim.
Whether Prospect Lake 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 Prospect Lake
These are the measurements Colorado WQCD publishes for Prospect Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 300 µg/L. Chlorophyll-a 42.5 µg/L. TSI 77.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 300µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 42.5µg/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. | 77 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Prospect Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~18 ft est.
Surface area
398 acres
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Colorado has not published bathymetry for Prospect Lake.
Lake Size & Watershed
Watershed (drainage) area
10 sq mi
HydroLAKES / HydroSHEDS
Shoreline
4.1 mi
HydroLAKES / HydroSHEDS
Elevation
5,016 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.
Stays via Stay22
Stays near Prospect Lake
Compare lakeside cabins, hotels, and vacation rentals near Prospect Lake in Weld 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 Prospect Lake are listed below.
Top-rated places to stay near Prospect Lake
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Fishing Prospect Lake
Water quality readings over time
3 seasons of samples on record (2020–2024). Calling a direction takes at least 4 years of the same measurement.
Phosphorus
Worsening+30.38 µg/L/yr3 years
Chlorophyll-a
Worsening+16.29 µg/L/yr3 years
Reservoir Info (USACE NID)
Prospect Lake is a man-made reservoir impounded by the Prospect (completed 1914), built primarily for irrigation on the Lost Creek-Tr; earth-type dam, 45 ft tall and 5,301 ft long.
- Surface area
- 398 ac
- Normal storage
- 6,368 ac-ft
- Max storage
- 9,299 ac-ft
- Drainage area
- 9 sq mi
- Hazard class
- Significant
- Owner
- HENRYLYN IRRIGATION DISTRICT
Source: USACE National Inventory of Dams, NID ID CO01106 · Operator website
EPA Impairment Status
Prospect Lake 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: Aquatic life.
Source: EPA ATTAINS assessment unit COSPMS07_B · Official waterbody report
Nearby Lakes in Weld County
Frequently asked questions about Prospect Lake
Where is Prospect Lake?
- Prospect Lake is a lake in Weld County, Colorado. Its water-quality measurements are published by Colorado WQCD and shown on this page as reported.
What is the water quality of Prospect Lake?
- Prospect Lake in Weld County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Phosphorus: 300 µg/L. Chlorophyll-a (algae): 42.5 µg/L. Surface area: 398 acres.
Is Prospect Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Prospect Lake is listed impaired under Clean Water Act §303(d) (IR 5) for pH / acidity. Check local advisories before you swim.
How deep is Prospect Lake?
- No published bathymetric survey covers Prospect Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 18 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 398 acres.
Explore Prospect Lake across LakeQuality
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Where this data comes from
55 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Metro Water Recovery (formerly Metro Wastewater Reclamation District)
MWRD_WQX55 samples · 2020–2024
Analytical methods
- 4500 P H ~ Manual Digestion and Flow Injection Analysis for Total Phosphorus
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity by Nephelometry
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)