Colby Lake
Colby Lake in Washington County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3.8 ft visibility. Phosphorus: 61 µg/L. Chlorophyll-a (algae): 34.5 µg/L. Maximum depth: 11 ft. Surface area: 70.94 acres.
- Clarity
- 3.8 ft
- Typical in August
- 74°F
- Max depth
- 11 ft
- Area
- 71 acres
- Type
- Eutrophic
- Public access
- No
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Colby Lake →
Next lake in Washington County
Colby Lake is a 71-acre productive, nutrient-rich eutrophic lake in Washington County, Minnesota with a maximum depth of 11 feet (7-foot average). Water quality is graded F based on 2 sampling years through 2024. The lake supports 8 documented fish species including black bullhead, black crappie, and bluegill. No public access — the lake is private or restricted. Compared to the 74 other monitored lakes in Washington County, Colby Lake ranks #66 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-22. Grade methodology: LakeGrade methodology.
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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.
Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom
Water Quality Grade: F (Algae-prone)
Murky, only visible to about 3.8 ft. Phosphorus level: 61 µg/L. Chlorophyll-a: 34.5 µg/L. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.8 ft | Not graded |
| Phosphorus | 61 µg/L | Poor |
| Chlorophyll-a (Algae) | 34.5 µg/L | Poor |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Colby Lake
Compare lakeside cabins, hotels, and vacation rentals near Colby Lake in Washington County, Minnesota — 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Colby Lake are listed below.
Top-rated places to stay near Colby Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Colby Lake typically sits around 74°F at the surface in August. Summer average is about 73°F. Usually warmest in Jul (about 76°F) and coldest in Apr (about 54°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 83 field readings (2011–2024) via the EPA Water Quality Portal. See the full Colby Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 11 ft |
| Average Depth | 7 ft |
| Surface Area | 71 acres |
| Shoreline Length | 2.3 mi |
| Littoral Zone | 97% |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Colby Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
EPA Impairment Status
Colby Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MN82-0094-00 · Official waterbody report
County Ranking
Ranked #66 of 75 lakes in Washington County
Nearby Lakes With Higher Grades
Colby Lake holds Grade F. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Washington County
Frequently asked questions about Colby Lake
What is the water quality grade for Colby Lake?
- Colby Lake in Washington County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3.8 ft visibility. Phosphorus: 61 µg/L. Chlorophyll-a (algae): 34.5 µg/L. Maximum depth: 11 ft. Surface area: 70.94 acres.
Is Colby Lake safe to swim in?
- Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom. Colby Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 34.5 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Colby Lake?
- Colby Lake typically sits around 74°F at the surface in August, from 83 EPA Water Quality Portal field readings (2011–2024). That is a typical value for the month, not a live reading.
How deep is Colby Lake?
- Colby Lake has a maximum depth of 11 feet and an average depth of 7 feet. The lake covers 70.94 acres.
What fish are in Colby Lake?
- Fish species found in Colby Lake include black bullhead, black crappie, bluegill, channel catfish, green sunfish, hybrid sunfish, pumpkinseed, yellow perch. Colby Lake is located in Washington County, Minnesota.
Explore Colby Lake across LakeGrade
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High nutrients, frequent algae, reduced clarity
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Where this data comes from
56 measurements from 1 monitoring station, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA56 samples · 2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- Analysis of Chlorophyll in Periphyton and Plankton
Monitoring station identifiers (1)
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)
Lake details from Minnesota DNR LakeFinder