Carter Reservoir
Larimer County, Colorado3,551 acresView mapDirections
Not enough samples to grade — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). No letter yet. Here is what we do have.
- 81 ft max depth
- Limited data
Carter Reservoir in Larimer County, Colorado is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 3551 acres.
- Max depth
- ~81 ft est.
- Area
- 3,551 acres
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Watch Carter Reservoir’s letter
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Why Carter Reservoir has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Carter Reservoir, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by CDPHE and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Carter Reservoir is a 3,551-acre lake in Larimer County, Colorado with an estimated average depth of about 81 feet.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2022-10-27. Grade methodology: LakeQuality methodology.
What Carter Reservoir is good for
From access and monitoring records, not editorial picks.
- Big water3,551 acres
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Carter Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, metals (other than mercury). Check local advisories before you swim.
Water quality measurements for Carter Reservoir
These readings exist but are not enough for an A–F grade — see why.
No clarity data.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples |
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~81 ft est. |
| Surface Area | 3,551 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 Carter Reservoir.
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 Carter Reservoir
Reservoir Info (USACE NID)
Carter Reservoir is a man-made reservoir impounded by the Carter Lake Dam 1 (completed 1952), built primarily for hydroelectric on the Big Thompson River Os; earth-type dam, 214 ft tall and 1,235 ft long.
- Surface area
- 3,551 ac
- Normal storage
- 112,228 ac-ft
- Max storage
- 116,837 ac-ft
- Drainage area
- 18.03 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Hydroelectric;Irrigation;Water Supply.
Source: USACE National Inventory of Dams, NID ID CO01650 · Operator website
EPA Impairment Status
Carter Reservoir 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 COSPBT11_A · Official waterbody report
Graded lakes near Carter Reservoir
Carter Reservoir has no grade, but these lakes within a short drive do.
Nearby Lakes in Larimer County
Frequently asked questions about Carter Reservoir
Where is Carter Reservoir?
- Carter Reservoir is a lake in Larimer County, Colorado. LakeQuality has not rated this lake (UNRATED) — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
What is the water quality grade for Carter Reservoir?
- Carter Reservoir in Larimer County, Colorado is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 3551 acres.
Is Carter Reservoir safe to swim in?
- The letter is not a swimming clearance. Carter Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, metals (other than mercury). Check local advisories before you swim.
How deep is Carter Reservoir?
- No published bathymetric survey covers Carter Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 81 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 3551 acres.
Explore Carter Reservoir across LakeQuality
Planning a trip around Rocky Mountain?
Carter Reservoir is about 25 miles from Rocky Mountain 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 Rocky Mountain →More Colorado Lake Rankings
Other Lakes in Colorado
Where this data comes from
6 measurements from 2 monitoring stations, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Colorado Dept. of Public Health & Environment-WQCD
21COL001_WQX6 samples · 2022
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)
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)