Horse Creek Outlet Lake
Weld County, Colorado712 acresView mapDirections
Nutrients and algae run above the regional average.
- Eutrophic
- #3 of 5 in the county
- 56 ft max depth
Horse Creek Outlet Lake in Weld County, Colorado has a water quality grade of D (Nutrient-rich). Phosphorus: 460 µg/L. Chlorophyll-a (algae): 27.6 µg/L. Surface area: 712 acres.
- Max depth
- ~56 ft est.
- Area
- 712 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
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Watch Horse Creek Outlet Lake’s letter
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Horse Creek Outlet Lake is a 712-acre productive, nutrient-rich eutrophic lake in Weld County, Colorado with an estimated average depth of about 56 feet. Water quality is graded D based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 4 other monitored lakes in Weld County, Horse Creek Outlet Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2024-08-28. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyAlgae risk
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The D is nutrients and algae, not a swimming clearance. Horse Creek Outlet Lake is listed impaired under Clean Water Act §303(d) (IR 5) for pH / acidity. Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
No clarity data. Phosphorus 460 µg/L. Chlorophyll-a 27.6 µg/L. TSI 78. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 460 µg/L | Poor |
| Chlorophyll-a (Algae) | 27.6 µg/L | Poor |
| Trophic State Index (TSI) | 78 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~56 ft est. |
| Average Depth | ~33 ft est. |
| Surface Area | 712 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 Horse Creek Outlet Lake.
Lake Size & Watershed
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.
Fishing Horse Creek Outlet Lake
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | → Stable | -7.29 µg/L/yr | 4 |
| Chlorophyll-a | ↓ Declining | +8.85 µg/L/yr | 4 |
Reservoir Info (USACE NID)
Horse Creek Outlet Lake is a man-made reservoir impounded by the Horse Creek (completed 1910), built primarily for irrigation on the Horse Creek; earth-type dam, 39 ft tall and 4,800 ft long.
- Surface area
- 712 ac
- Normal storage
- 15,537 ac-ft
- Max storage
- 29,739 ac-ft
- Drainage area
- 26 sq mi
- Hazard class
- High
- Owner
- HENRYLYN IRRIGATION DISTRICT
Source: USACE National Inventory of Dams, NID ID CO00012 · Operator website · Matched by proximity (0.52 km)
EPA Impairment Status
Horse Creek Outlet Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit COSPMS07_C · Official waterbody report · Matched by proximity (1.53 km)
County Ranking
Ranked #3 of 5 lakes in Weld County
Nearby Lakes in Weld County
Frequently asked questions about Horse Creek Outlet Lake
Where is Horse Creek Outlet Lake?
- Horse Creek Outlet Lake is a lake in Weld County, Colorado. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Horse Creek Outlet Lake?
- Horse Creek Outlet Lake in Weld County, Colorado has a water quality grade of D (Nutrient-rich). Phosphorus: 460 µg/L. Chlorophyll-a (algae): 27.6 µg/L. Surface area: 712 acres.
Is Horse Creek Outlet Lake safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Horse Creek Outlet Lake is listed impaired under Clean Water Act §303(d) (IR 5) for pH / acidity. Check local advisories before you swim.
How deep is Horse Creek Outlet Lake?
- No published bathymetric survey covers Horse Creek Outlet Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 56 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 712 acres.
Explore Horse Creek Outlet Lake across LakeQuality
More Colorado Lake Rankings
Other Grade D Lakes in Colorado
Eutrophic Lakes in Colorado
Where this data comes from
78 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_WQX78 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)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)