Knife Lake
Knife Lake in Kanabec County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 2 ft visibility. Phosphorus: 161.5 µg/L. Chlorophyll-a (algae): 97.2 µg/L. Maximum depth: 15 ft. Surface area: 1259.24 acres.
- Clarity
- 2 ft
- Typical in August
- 73°F
- Max depth
- 15 ft
- Area
- 1,259 acres
- Type
- Hypereutrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 12
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Knife Lake →
Next lake in Kanabec County
Free interactive depth-contour map of Knife Lake, reaching a maximum surveyed depth of 15 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Knife Lake is a 1,259-acre highly nutrient-loaded hypereutrophic lake in Kanabec County, Minnesota with a maximum depth of 15 feet (9-foot average). Water quality is graded F based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 19 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 2 public boat landings. Compared to the 1 other monitored lakes in Kanabec County, Knife Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-23. Grade methodology: LakeGrade methodology.
Watch Knife Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
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 2 ft of visibility. Phosphorus level: 161.5 µg/L. Chlorophyll-a: 97.2 µg/L. Trophic State Index: 73.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2 ft | Not graded |
| Phosphorus | 161.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 97.2 µg/L | Poor |
| Trophic State Index (TSI) | 73 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Knife Lake
Compare lakeside cabins, hotels, and vacation rentals near Knife Lake in Kanabec 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 Knife Lake are listed below.
Top-rated places to stay near Knife Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Knife Lake typically sits around 73°F at the surface in August. Summer average is about 73°F. Usually warmest in Jul (about 78°F) and coldest in May (about 62°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 32 field readings (2010–2023) via the EPA Water Quality Portal. See the full Knife Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Knife Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (469,894 cells/mL) on July 19, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 15 ft |
| Average Depth | 9.1 ft |
| Surface Area | 1,259 acres |
| Shoreline Length | 18.2 mi |
| Littoral Zone | 100% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Knife Lake (South)Public
- Knife Lake (North)Public
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Knife Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
DNR Fisheries Survey Summary
22 surveys on file from MN DNR Fisheries. Most recent: 2025-10-20 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Walleye | 52.65 | 1.51 lb |
| SUN | 40.17 | — |
| Common Carp | 20.08 | 1.09 lb |
| Largemouth Bass | 17.64 | 0.87 lb |
| White Crappie | 16.85 | 0.28 lb |
| Yellow Perch | 13.14 | 0.2 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
Largemouth Bass
Yellow Perch
From the 2025-10-20 survey
Knife Lake is a 1,266-acre lake in central Kanabec County located six miles north of Mora and is within the Snake River Watershed. The lake has a maximum depth of 16 ft and 99% of the lake is 15 feet or less (1,259 littoral acres). Knife River flows originate from groundwater, which allows cool water species such as…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Knife Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — KnifeFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Knife (0283)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — KnifeFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — KnifePublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.019 m/yr | 6 |
| Phosphorus | → Stable | -0.7 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +6.07 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (46 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2012-03-21 (2012) | 2013-05-07 (2013) |
| Ice-In | 1992-11-15 (1992) | 2004-11-24 (2004) |
Most recent ice-out: 2025-03-31
Reservoir Info (USACE NID)
Knife Lake is a man-made reservoir impounded by the Knife Lake (completed 1983), built primarily for recreation on the Knife River; buttress-type dam, 22 ft tall and 725 ft long.
- Surface area
- 1,277 ac
- Normal storage
- 8,272 ac-ft
- Max storage
- 11,374 ac-ft
- Drainage area
- 92 sq mi
- Hazard class
- Significant
- Owner
- County of Kanabec;LID of Knife Lake;SWCD of Kanabec
Source: USACE National Inventory of Dams, NID ID MN00400 · Operator website
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 MN33-0028-00 · Official waterbody report
County Ranking
Ranked #2 of 2 lakes in Kanabec County
Nearby Lakes With Higher Grades
Knife Lake holds Grade F. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Kanabec County
Frequently asked questions about Knife Lake
What is the water quality grade for Knife Lake?
- Knife Lake in Kanabec County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 2 ft visibility. Phosphorus: 161.5 µg/L. Chlorophyll-a (algae): 97.2 µg/L. Maximum depth: 15 ft. Surface area: 1259.24 acres.
Is Knife 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. Knife Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 97.2 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Knife Lake?
- Knife Lake typically sits around 73°F at the surface in August, from 32 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
How deep is Knife Lake?
- Knife Lake has a maximum depth of 15 feet and an average depth of 9.1 feet. The lake covers 1259.24 acres.
What fish are in Knife Lake?
- Fish species found in Knife Lake include black bullhead, black crappie, bluegill, brown bullhead, golden redhorse, greater redhorse, green sunfish, hybrid sunfish, largemouth bass, northern hog sucker, northern pike, pumpkinseed, rock bass, shorthead redhorse, smallmouth bass, walleye, white sucker, yellow bullhead, yellow perch. Knife Lake is located in Kanabec County, Minnesota.
When does Knife Lake thaw?
- Knife Lake typically has ice-out around Apr 12.
Does Knife Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Knife Lake (clouds, ice, or an off-season gap). The most recent reading was high (469,894 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Knife Lake?
- Knife Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Knife Lake (South), Knife Lake (North). Public access is listed as yes.
Explore Knife Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Kanabec County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Rum River Watershed, ranked by water quality
Very high nutrients, dense algae, poor clarity
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Knife Lake
Other Grade F Lakes in Minnesota
Hypereutrophic Lakes in Minnesota
Compare Knife Lake With Nearby Lakes
Where this data comes from
86 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA86 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (2)
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
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate