Lake John
Jackson County, Colorado612 acresView mapDirections
Colorado WQCD publishes the water-quality measurements for Lake John. Here is what has been measured.
- Oligotrophic
- Impaired · Metals (other than mercury)
- 46 ft max depth
- Public access
- Limited data
Lake John in Jackson County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 13.8 ft visibility. Phosphorus: 18 µg/L. Chlorophyll-a (algae): 1.6 µg/L. Surface area: 612 acres.
Lake John is a 612-acre cold, clear oligotrophic lake in Jackson County, Colorado with an estimated average depth of about 46 feet. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2025-09-09. Methodology: how these readings are compared.
What Lake John is good for
From access and monitoring records, not editorial picks.
- Clear water13.8 ft of visibility
- Boat launch1 documented ramp
Swimming conditions
Readings onlyLimited data
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. Lake John is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury), pH / acidity. Check local advisories before you swim.
Whether Lake John 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 Lake John
These are the measurements Colorado WQCD publishes for Lake John, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 13.8 ft. Phosphorus 18 µg/L. Chlorophyll-a 1.6 µg/L. TSI 40.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 13.8ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 18µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 1.6µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 40 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Lake John
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~46 ft est.
Surface area
612 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 Lake John.
Lake Size & Watershed
Watershed (drainage) area
2 sq mi
HydroLAKES / HydroSHEDS
Shoreline
5.1 mi
HydroLAKES / HydroSHEDS
Elevation
8,068 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
- Lake John State Wildlife AreaPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
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Stays near Lake John
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Fishing Lake John
Reservoir Info (USACE NID)
Lake John is a man-made reservoir impounded by the Lake John (completed 1957), built primarily for recreation on the N Fk North Platte-Tr; earth-type dam, 27 ft tall and 1,723 ft long.
- Surface area
- 612 ac
- Normal storage
- 7,092 ac-ft
- Max storage
- 16,128 ac-ft
- Drainage area
- 2 sq mi
- Hazard class
- Significant
- Owner
- COLORADO PARKS AND WILDLIFE
All listed purposes: Recreation;Fish and Wildlife Pond.
Source: USACE National Inventory of Dams, NID ID CO00993 · Operator website
EPA Impairment Status
Lake John 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 COUCNP09_D · Official waterbody report
Nearby Lakes in Jackson County
Frequently asked questions about Lake John
Where is Lake John?
- Lake John is a lake in Jackson County, Colorado. Its water-quality measurements are published by Colorado WQCD and shown on this page as reported.
What is the water quality of Lake John?
- Lake John in Jackson County, Colorado has water-quality measurements published by Colorado WQCD, shown here as reported. Water clarity: 13.8 ft visibility. Phosphorus: 18 µg/L. Chlorophyll-a (algae): 1.6 µg/L. Surface area: 612 acres.
Is Lake John safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Lake John is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury), pH / acidity. Check local advisories before you swim.
How deep is Lake John?
- No published bathymetric survey covers Lake John, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 46 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 612 acres.
Are there boat ramps on Lake John?
- Lake John has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Lake John State Wildlife Area. Public access is listed as yes.
Can I fish at Lake John?
- Lake John has 1 documented boat landing 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 Lake John across LakeQuality
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Where this data comes from
8 measurements from 2 monitoring stations, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Colorado Dept. of Public Health & Environment-WQCD
21COL001_WQX8 samples · 2021–2025
Analytical methods
- Secchi disk depth measurement
- 10200 H ~ Chlorophyll a-b-c Determination
- Phosphorus by Colorimetry
- 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