Carp Lake
Unknown County, MinnesotaLimited DataMesotrophic
Carp Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.
A TSI near 46 places Carp Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. A maximum depth of 34 ft puts Carp Lake in the middle of Minnesota's depth distribution. The lake's 836 acres and 27.8 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Carp Lake ranks 4 of 5 in Unknown County — at the lower end of the locally monitored distribution.
No invasive species are currently listed at Carp Lake — the lake remains off the Minnesota infested-waters roster. The fishery includes walleye alongside the lake's other 10 documented species — a notable draw for Minnesota anglers. No formal public access is documented at Carp Lake — most use is by shoreline residents and their guests. 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 2025-07-26. Grade methodology: LakeGrade methodology.
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Moderate clarity, visible to about 8.5 ft. Trophic State Index: 46.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.5 ft | C |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 46 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 34 ft |
| Surface Area | 836 acres |
| Shoreline Length | 27.8 mi |
| Littoral Zone | 41% |
| Public Access | No |
Fish Species
Click a species to see every graded lake where it is documented.
→ Best fishing times for Carp Lake (14-day solunar calendar)
→ Is it safe to eat fish from Carp Lake? (mercury & PFAS guide)
→ Carp 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 | +0.049 m/yr | 5 |
Location
County Ranking
Ranked #4 of 5 lakes in Unknown County
Nearby Lakes in Unknown County
More Minnesota Lake Rankings
Other Grade C Lakes in Minnesota
Mesotrophic Lakes in Minnesota
Compare Carp Lake With Nearby Lakes
DNR Fisheries Survey Summary
9 surveys on file from MN DNR Fisheries. Most recent: 2017-09-05 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Walleye | 7.49 | 1.61 lb |
| Tullibee (Cisco) | 6.15 | 0.64 lb |
| White Sucker | 4.19 | 2.8 lb |
| CIS | 3.50 | 0.57 lb |
| Bluegill | 2.35 | 0.19 lb |
| Northern Pike | 2.28 | 3.61 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.
Walleye
Tullibee (Cisco)
White Sucker
CIS
From the 2017-09-05 survey
Birch Lake is located approximately 18 miles NE of Ely within the BWCAW. The northern half of the lake is part of Ontario's Quetico Provincial Park. Birch Lake is 836 acres with 397 of these acres in Minnesota. Visitors should be familiar with appropriate regulations when traveling these wilderness areas. Birch Lake…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Carp Lake. 1 report on file.
- —Fisheries Lake Survey — BirchFisheries Lake Survey · MN DNR LakeFinder
EPA Impairment Status
Carp 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 MN38-0491-00 · Official waterbody report · Matched by proximity (2.62 km)
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Lake details from Minnesota DNR LakeFinder
Most recent sample: 2025-07-26
Monitoring stations: 8
Where to stay near Carp Lake
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