John Martin Reservoir
Bent County, Colorado11,590 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.
- 60 ft max depth
- Public access
- Limited data
John Martin Reservoir in Bent County, Colorado is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 3.1 ft visibility. Phosphorus: 53 µg/L. Chlorophyll-a (algae): 16.5 µg/L. Surface area: 11590 acres.
- Clarity
- 3.1 ft
- Max depth
- ~60 ft est.
- Area
- 11,590 acres
- Public access
- Yes
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Watch John Martin Reservoir’s letter
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Why John Martin 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 John Martin Reservoir, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded water clarity, phosphorus and algae (chlorophyll-a).
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.
John Martin Reservoir is a 11,590-acre lake in Bent County, Colorado with an estimated average depth of about 60 feet. Limited fish-species data available. Public access is available with 3 public boat landings.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2023-08-08. Grade methodology: LakeQuality methodology.
What John Martin Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch3 documented ramps
- Big water11,590 acres
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Check local advisories before you swim.
Water quality measurements for John Martin Reservoir
These readings exist but are not enough for an A–F grade — see why.
Very murky, less than 3.1 ft of visibility. Phosphorus 53 µg/L. Chlorophyll-a 16.5 µg/L. TSI 60.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.1 ft | Not graded |
| Phosphorus | 53 µg/L | Not graded |
| Chlorophyll-a (Algae) | 16.5 µg/L | Not graded |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
→ John Martin Reservoir water level: the live USGS gauge reading
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~60 ft est. |
| Average Depth | ~56 ft est. |
| Surface Area | 11,590 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Colorado has not published bathymetry for John Martin 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.
Recreation & Access
- John Martin State Wildlife AreaPublic
- John Martin Reservoir State ParkPublic
- John Martin Reservoir State ParkPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing John Martin Reservoir
Reservoir Info (USACE NID)
John Martin Reservoir is a man-made reservoir impounded by the John Martin Dam (completed 1943), built primarily for flood risk reduction on the Arkansas; gravity-type dam, 25 ft tall and 13,000 ft long.
- Surface area
- 11,590 ac
- Normal storage
- 345,250 ac-ft
- Max storage
- 608,245 ac-ft
- Drainage area
- 0 sq mi
- Hazard class
- High
- Owner
- USACE - Albuquerque District
All listed purposes: Flood Risk Reduction;Other;Irrigation.
Source: USACE National Inventory of Dams, NID ID CO01283 · Operator website
Nearby Lakes in Bent County
Frequently asked questions about John Martin Reservoir
Where is John Martin Reservoir?
- John Martin Reservoir is a lake in Bent 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 John Martin Reservoir?
- John Martin Reservoir in Bent County, Colorado is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 3.1 ft visibility. Phosphorus: 53 µg/L. Chlorophyll-a (algae): 16.5 µg/L. Surface area: 11590 acres.
Is John Martin Reservoir safe to swim in?
- The letter is not a swimming clearance. Check local advisories before you swim.
How deep is John Martin Reservoir?
- No published bathymetric survey covers John Martin Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 60 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 11590 acres.
Are there boat ramps on John Martin Reservoir?
- John Martin Reservoir has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include John Martin State Wildlife Area, John Martin Reservoir State Park, John Martin Reservoir State Park. Public access is listed as yes.
Explore John Martin Reservoir across LakeQuality
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Where this data comes from
6 measurements from 2 monitoring stations, 2023. 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 · 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 (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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory