Lake John
Jackson County, Colorado612 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Oligotrophic
- #1 of 1 in the county
- 46 ft max depth
- Public access
- Limited data
Lake John in Jackson County, Colorado has a water quality grade of A (Excellent). Water clarity: 13.8 ft visibility. Phosphorus: 18 µg/L. Chlorophyll-a (algae): 1.6 µg/L. Surface area: 612 acres.
- Clarity
- 13.8 ft
- Max depth
- ~46 ft est.
- Area
- 612 acres
- Type
- Oligotrophic
- Public access
- Yes
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Watch Lake John’s letter
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Lake John is a 612-acre cold, clear oligotrophic lake in Jackson County, Colorado with an estimated average depth of about 46 feet. Water quality is graded A based on 1 sampling years through 2025. 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. Grade methodology: LakeQuality methodology.
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 Safety
Grade onlyLimited data
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 A is nutrients and algae, 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.
Water Quality Grade: A (Excellent)
Good clarity, visible to about 13.8 ft. Phosphorus 18 µg/L. Chlorophyll-a 1.6 µg/L. TSI 40. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13.8 ft | Not graded |
| Phosphorus | 18 µg/L | Not graded |
| Chlorophyll-a (Algae) | 1.6 µg/L | Good |
| Trophic State Index (TSI) | 40 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~46 ft est. |
| Average Depth | ~18 ft est. |
| Surface Area | 612 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 Lake John.
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
- Lake John State Wildlife AreaPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
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
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit COUCNP09_D · Official waterbody report
County Ranking
Ranked #1 of 1 lakes in Jackson County
Nearby Lakes in Jackson County
Frequently asked questions about Lake John
Where is Lake John?
- Lake John is a lake in Jackson County, Colorado. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake John?
- Lake John in Jackson County, Colorado has a water quality grade of A (Excellent). 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?
- The A is nutrients and algae, 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.
Explore Lake John across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Colorado's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
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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)
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)
Named boat-access points from the USGS National Boat Ramps inventory