Mayhew Lake
Mayhew Lake in Cook County, Minnesota has a water quality grade of A (Excellent). Water clarity: 20.6 ft visibility. Phosphorus: 5 µg/L. Chlorophyll-a (algae): 1.5 µg/L. Maximum depth: 84 ft. Surface area: 220.9 acres.
- Clarity
- 20.6 ft
- Typical in August
- 56°F
- Max depth
- 84 ft
- Area
- 221 acres
- Type
- Oligotrophic
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Cook County
Mayhew Lake is a 221-acre cold, clear oligotrophic lake in Cook County, Minnesota with a maximum depth of 84 feet (33-foot average). Water quality is graded A based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. The lake supports 8 documented fish species including bluegill, green sunfish, and hybrid sunfish. Public access is available. Compared to the 43 other monitored lakes in Cook County, Mayhew Lake ranks #18 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-08-20. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Crystal clear, you can see 20.6 ft down. Phosphorus level: 5 µg/L. Chlorophyll-a: 1.5 µg/L. Trophic State Index: 32.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 20.6 ft | Not graded |
| Phosphorus | 5 µg/L | Good |
| Chlorophyll-a (Algae) | 1.5 µg/L | Good |
| Trophic State Index (TSI) | 32 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Mayhew Lake
Compare lakeside cabins, hotels, and vacation rentals near Mayhew Lake in Cook 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.
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Water Temperature
Mayhew Lake typically sits around 56°F at the surface in August. Summer average is about 55°F. Usually warmest in Jun (about 56°F) and coldest in Jul (about 54°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 300 field readings (2011–2024) via the EPA Water Quality Portal. See the full Mayhew Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 84 ft |
| Average Depth | 32.5 ft |
| Surface Area | 221 acres |
| Shoreline Length | 5 mi |
| Littoral Zone | 15% |
| Public Access | Yes |
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 Mayhew Lake
DNR Fisheries Survey Summary
6 surveys on file from MN DNR Fisheries. Most recent: 2023-07-08 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Yellow Perch | 26.76 | 0.09 lb |
| Bluegill | 4.87 | 0.05 lb |
| White Sucker | 4.04 | 1.3 lb |
| Bluntnose Minnow | 3.88 | — |
| Lake Trout | 2.94 | 1.35 lb |
| Rainbow Trout | 1.83 | 0.81 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
Length Distributions
Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.
Yellow Perch
Bluegill
White Sucker
Lake Trout
From the 2023-07-08 survey
Mayhew Lake is a 220-acre lake located 35 miles north of Grand Marais. It lies in the headwaters of the Rainy River, draining to that system via Loon, Crab, and Gunflint Lakes into the Granite River. There is a public carry-in access on the southeast corner of the lake. Mayhew Lake has been managed primarily for lake…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Mayhew Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — MayhewFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Mayhew (1833)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — MayhewFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — MayhewPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.078 m/yr | 5 |
| Phosphorus | ↑ Improving | -0.15 µg/L/yr | 5 |
| Chlorophyll-a | ↑ Improving | -0.06 µg/L/yr | 5 |
EPA Impairment Status
Mayhew 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 MN16-0337-00 · Official waterbody report
County Ranking
Ranked #18 of 44 lakes in Cook County
Nearby Lakes in Cook County
Frequently asked questions about Mayhew Lake
What is the water quality grade for Mayhew Lake?
- Mayhew Lake in Cook County, Minnesota has a water quality grade of A (Excellent). Water clarity: 20.6 ft visibility. Phosphorus: 5 µg/L. Chlorophyll-a (algae): 1.5 µg/L. Maximum depth: 84 ft. Surface area: 220.9 acres.
Is Mayhew Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Mayhew Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 1.5 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Mayhew Lake?
- Mayhew Lake typically sits around 56°F at the surface in August, from 300 EPA Water Quality Portal field readings (2011–2024). That is a typical value for the month, not a live reading.
How deep is Mayhew Lake?
- Mayhew Lake has a maximum depth of 84 feet and an average depth of 32.5 feet. The lake covers 220.9 acres.
What fish are in Mayhew Lake?
- Fish species found in Mayhew Lake include bluegill, green sunfish, hybrid sunfish, lake trout, northern pike, rainbow trout, white sucker, yellow perch. Mayhew Lake is located in Cook County, Minnesota.
Explore Mayhew Lake across LakeGrade
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Where this data comes from
51 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA51 samples · 2020–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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