John Martin Reservoir
Bent County, Colorado11,590 acresView mapDirections
Colorado WQCD publishes the water-quality measurements for John Martin Reservoir. Here is what has been measured.
- Impaired · Metals (other than mercury)
- 60 ft max depth
- Public access
- Limited data
John Martin Reservoir in Bent County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 3.1 ft visibility. Phosphorus: 53 µg/L. Chlorophyll-a (algae): 16.5 µg/L. Surface area: 11590 acres.
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. Methodology: how these readings are compared.
At about 12,000 acres, John Martin Reservoir is large enough that where you stay decides which shore you see most of. It has 3 public boat landings, so a lakefront rental is not the only way to get a boat on the water. Vrbo is where to look for cabins and lake homes around John Martin Reservoir, and Booking.com and Expedia search hotels near the lake for your dates.
What John Martin Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch3 documented ramps
- Big water11,590 acres
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. John Martin Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury). Check local advisories before you swim.
Whether John Martin Reservoir 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 John Martin Reservoir
These are the measurements Colorado WQCD publishes for John Martin Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 3.1 ft of visibility. Phosphorus 53 µg/L. Chlorophyll-a 16.5 µg/L. TSI 60.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 3.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 53µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 16.5µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 60 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about John Martin Reservoir
Answers come straight from the public measurements and survey records on this page.
→ John Martin Reservoir water level: the live USGS gauge reading
Lake Details
Max depth
~60 ft est.
Surface area
11,590 acres
Public access
Yes
Listed by Colorado WQCD
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
Watershed (drainage) area
18,409 sq mi
HydroLAKES / HydroSHEDS
Shoreline
38.2 mi
HydroLAKES / HydroSHEDS
Elevation
3,842 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.
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
Stays via Stay22
Stays near John Martin Reservoir
Compare lakeside cabins, hotels, and vacation rentals near John Martin Reservoir in Bent 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 John Martin Reservoir
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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
EPA Impairment Status
John Martin Reservoir 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, Aquatic life.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit COARLA11_A · Official waterbody report
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. Its water-quality measurements are published by Colorado WQCD and shown on this page as reported.
What is the water quality of John Martin Reservoir?
- John Martin Reservoir in Bent County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. John Martin Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury). 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.
Can I fish at John Martin Reservoir?
- John Martin Reservoir has 3 documented boat landings in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Colorado's fish and wildlife agency, so check its current regulations before you go.
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)
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)
Named boat-access points from the USGS National Boat Ramps inventory