Knife Lake
Lake County, MinnesotaLimited DataOligotrophic
On the LakeGrade rubric, Knife Lake pulls an A: clarity at 20.0 ft and phosphorus readings still being added put it in the top bracket for Minnesota.
A TSI value of 34 puts Knife Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. Knife Lake is a shallow lake at 11 ft maximum depth, which means it warms quickly, mixes constantly, and amplifies nutrient inputs. At 105 acres, Knife Lake fits the Minnesota median for monitored lakes, with 2.5 miles of shoreline. Among the 142 graded lakes in Lake County, Knife Lake ranks 6 — in the top quartile locally.
No invasive species are currently listed at Knife Lake — the lake remains off the Minnesota infested-waters roster. The state fisheries records do not list documented species for Knife Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The lake lacks a documented public access point, so visitor use is limited. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-06-18. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 20 ft down. Trophic State Index: 34.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 20 ft | A |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 34 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 11 ft |
| Surface Area | 104.9 acres |
| Shoreline Length | 2.5 mi |
| Littoral Zone | 100% |
| Public Access | No |
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.343 m/yr | 5 |
Location
County Ranking
Ranked #6 of 142 lakes in Lake County
Nearby Lakes in Lake County
More Minnesota Lake Rankings
Other Grade A Lakes in Minnesota
Oligotrophic Lakes in Minnesota
DNR Fisheries Survey Summary
1 survey on file from MN DNR Fisheries. Most recent: 1972-08-09 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| White Sucker | 6.20 | 1.66 lb |
| Northern Pike | 5.60 | 2.59 lb |
| Yellow Perch | 1.40 | 0.16 lb |
| Pumpkinseed | 1.00 | 0.06 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
From the 1972-08-09 survey
Good population of northern pike; however, most are small (2-4 lbs). Sucker population is high and yellow perch population is low.
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Knife Lake. 1 report on file.
- —Fisheries Lake Survey — BonnieFisheries Lake Survey · MN DNR LakeFinder
EPA Impairment Status
Knife 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 MN38-0404-00 · Official waterbody report
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: 2024-06-18
Monitoring stations: 37