Rat Lake
Aitkin County, MinnesotaLimited DataEutrophic
Rat Lake earns a D — measurements through 2024 show persistent nutrient pressure that limits clarity through the summer.
A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. Rat Lake reaches 21 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. Rat Lake covers 431 acres alongside 4.7 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Within the 53 graded lakes of Aitkin County, Rat Lake sits at rank 46, near the bottom of the county list.
No invasive species are currently listed at Rat Lake — the lake remains off the Minnesota infested-waters roster. Walleye are documented at Rat Lake, one of 13 fish species on record for the lake. The lake lacks a documented public access point, so visitor use is limited. Ice-out has been recorded 5 times at Rat Lake, with a median around Apr 12. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-28. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Murky, only visible to about 5 ft. Trophic State Index: 54.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 54 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 21 ft |
| Surface Area | 431.3 acres |
| Shoreline Length | 4.7 mi |
| Littoral Zone | 90% |
| Public Access | No |
Fish Species
Click a species to see all Minnesota and Wisconsin lakes where it is found.
→ Best fishing times for Rat Lake (14-day solunar calendar)
→ Is it safe to eat fish from Rat Lake? (mercury & PFAS guide)
→ Rat Lake fishing regulations (limits, seasons, special rules)
Water Quality Trend: → Stable
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.015 m/yr | 5 |
Ice Season
Historical ice data from Minnesota DNR (8 observations).
Estimated open water season: 225 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2012-03-21 (2012) | 2022-04-29 (2022) |
| Ice-In | 2002-11-18 (2002) | 2012-11-27 (2012) |
Most recent ice-out: 2022-04-29
Location
County Ranking
Ranked #46 of 53 lakes in Aitkin County
Cleaner Lakes Within 30 Miles
Rat Lake holds Grade D. One nearby lake has a higher grade.
Nearby Lakes in Aitkin County
More Minnesota Lake Rankings
State Parks Near Rat Lake
Other Grade D Lakes in Minnesota
Eutrophic Lakes in Minnesota
DNR Fisheries Survey Summary
11 surveys on file from MN DNR Fisheries. Most recent: 2022-07-08 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| GOS | 22.65 | — |
| Bluegill | 14.07 | 0.29 lb |
| Yellow Perch | 8.27 | 0.18 lb |
| Largemouth Bass | 6.83 | 1.55 lb |
| Northern Pike | 3.28 | 1.57 lb |
| Black Crappie | 3.03 | 0.35 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.
Bluegill
Yellow Perch
Largemouth Bass
Northern Pike
From the 2022-07-08 survey
A targeted survey of nearshore fish species in Rat Lake was conducted on July 8, 2022 by Aitkin Area Fisheries Staff. Sampling sites were evenly spaced around the lake and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible. Backpack electrofishing was completed at…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Rat Lake. 3 reports on file.
- —Fisheries Lake Survey — RatFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Rat (0142)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — RatFish Stocking History · MN DNR LakeFinder
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate
Most recent sample: 2024-09-28
Monitoring stations: 1