Cowley Lake
Cowley Lake in Hennepin County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 0.8 ft visibility. Phosphorus: 738.6 µg/L. Chlorophyll-a (algae): 343.5 µg/L.
- Clarity
- 0.8 ft
- Typical in August
- 70°F
- Type
- Hypereutrophic
- Trend
- ↑ Improving
- Public access
- No
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Cowley Lake →
Next lake in Hennepin County
Cowley Lake is a highly nutrient-loaded hypereutrophic lake in Hennepin County, Minnesota. Water quality is graded F based on 3 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 80 other monitored lakes in Hennepin County, Cowley Lake ranks #80 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-01. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyAlgae risk
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)
Very murky, less than 0.8 ft of visibility. Phosphorus level: 738.6 µg/L. Chlorophyll-a: 343.5 µg/L. Trophic State Index: 89.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 0.8 ft | Not graded |
| Phosphorus | 738.6 µg/L | Poor |
| Chlorophyll-a (Algae) | 343.5 µg/L | Poor |
| Trophic State Index (TSI) | 89 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Cowley Lake
Compare lakeside cabins, hotels, and vacation rentals near Cowley Lake in Hennepin 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 Cowley Lake are listed below.
Top-rated places to stay near Cowley Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Cowley Lake typically sits around 70°F at the surface in August. Summer average is about 71°F. Usually warmest in Jul (about 72°F) and coldest in May (about 61°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 57 field readings (2023–2024) via the EPA Water Quality Portal. See the full Cowley Lake water temperature breakdown →
Fishing Cowley Lake
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Cowley Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fish Stocking History — CowleyFish Stocking History · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.06 m/yr | 2 |
| Phosphorus | ↑ Improving | -80.1 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -36 µg/L/yr | 2 |
EPA Impairment Status
Cowley Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN27-0169-00 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Cowley Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 1 facility has a reported Clean Water Act violation in the past three years.
- Met Council - Rogers WrrfRogers · 1.5 mi away · NPDES MN0029629MajorRecent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #80 of 81 lakes in Hennepin County
Nearby Lakes With Higher Grades
Cowley Lake holds Grade F. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Hennepin County
Frequently asked questions about Cowley Lake
What is the water quality grade for Cowley Lake?
- Cowley Lake in Hennepin County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 0.8 ft visibility. Phosphorus: 738.6 µg/L. Chlorophyll-a (algae): 343.5 µg/L.
Is Cowley 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. Cowley Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 343.5 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Cowley Lake?
- Cowley Lake typically sits around 70°F at the surface in August, from 57 EPA Water Quality Portal field readings (2023–2024). That is a typical value for the month, not a live reading.
Explore Cowley Lake across LakeGrade
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Where this data comes from
64 measurements from 1 monitoring station, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA64 samples · 2023–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 4500 N C ~ Persufate Method for Total Nitrogen
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)