Koronis Lake
Koronis Lake in Stearns County, Minnesota has a water quality grade of C (Fair). Water clarity: 6 ft visibility. Phosphorus: 27 µg/L. Chlorophyll-a (algae): 13.8 µg/L. Maximum depth: 132 ft. Surface area: 2968.28 acres.
- Clarity
- 6 ft
- Max depth
- 132 ft
- Area
- 2,968 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 14
- Open water
- 231 days
Next lake in Stearns County
Free interactive depth-contour map of Koronis Lake, reaching a maximum surveyed depth of 130 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Koronis Lake is a 2,968-acre productive, nutrient-rich eutrophic lake in Stearns County, Minnesota with a maximum depth of 132 feet (29-foot average). Water quality is graded C based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 22 documented fish species including bigmouth buffalo, black bullhead, and black crappie. Public access is available with 3 public boat landings. Compared to the 31 other monitored lakes in Stearns County, Koronis Lake ranks #11 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-15. Grade methodology: LakeGrade methodology.
Watch Koronis Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Murky, only visible to about 6 ft. Phosphorus level: 27 µg/L. Chlorophyll-a: 13.8 µg/L. Trophic State Index: 53.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6 ft | Not graded |
| Phosphorus | 27 µg/L | Fair |
| Chlorophyll-a (Algae) | 13.8 µg/L | Fair |
| Trophic State Index (TSI) | 53 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Koronis Lake
Compare lakeside cabins, hotels, and vacation rentals near Koronis Lake in Stearns 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.
Top-rated places to stay near Koronis 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 trip? Cabins and lodging at Koronis Lake → · more Minnesota lake trips
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Koronis Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (33,113 cells/mL) on June 12, 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 | 132 ft |
| Average Depth | 29 ft |
| Surface Area | 2,968 acres |
| Shoreline Length | 15.8 mi |
| Littoral Zone | 40% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Highway 55 BridgePublic
- Koronis Lake County ParkPublic
- Koronis Lake ParkPublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Koronis 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
31 surveys on file from MN DNR Fisheries. Most recent: 2025-10-23 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Yellow Perch | 33.36 | 0.13 lb |
| BKS | 31.70 | — |
| Walleye | 29.06 | 1.05 lb |
| Bluntnose Minnow | 16.84 | — |
| Bluegill | 14.58 | 0.17 lb |
| BLH | 12.89 | 0.51 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
Walleye
Bluegill
From the 2025-10-23 survey
A targeted fall night electrofishing survey was conducted for young of year "YOY" (fingerling sized) Walleye on Koronis during October 23, 2025. A targeted survey is generally used for sampling a specific kind of fish or time of year (i.e. spawning season, fall season, etc.) unlike a standard survey which samples a…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Koronis Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — Koronis (main lake)Fisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — Koronis (main lake)Fish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — Koronis (main lake)Public 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 | -0.111 m/yr | 6 |
| Phosphorus | ↓ Declining | +1.67 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +1.78 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (10 observations).
Estimated open water season: 231 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2004-04-03 (2004) | 2023-04-28 (2023) |
| Ice-In | 1977-11-29 (1977) | 1986-12-06 (1986) |
Most recent ice-out: 2023-04-28
Reservoir Info (USACE NID)
Koronis Lake is a man-made reservoir impounded by the Lake Koronis (completed 1989), built primarily for recreation on the Crow River; concrete-type dam, 9 ft tall.
- Surface area
- 3,034 ac
- Normal storage
- 9,112 ac-ft
- Max storage
- 90,000 ac-ft
- Drainage area
- 307 sq mi
- Hazard class
- Low
Source: USACE National Inventory of Dams, NID ID MN01547 · Operator website
EPA Impairment Status
Koronis Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN73-0200-02 · Official waterbody report · Matched by proximity (0.98 km)
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Koronis Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Ampi - PaynesvillePaynesville · 2.8 mi away · NPDES MN0044326Recent violation
- PaynesvillePaynesville · 2.8 mi away · NPDES MN0020168
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #11 of 32 lakes in Stearns County
Nearby Lakes With Higher Grades
Koronis Lake holds Grade C. 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 Stearns County
Frequently asked questions about Koronis Lake
What is the water quality grade for Koronis Lake?
- Koronis Lake in Stearns County, Minnesota has a water quality grade of C (Fair). Water clarity: 6 ft visibility. Phosphorus: 27 µg/L. Chlorophyll-a (algae): 13.8 µg/L. Maximum depth: 132 ft. Surface area: 2968.28 acres.
Is Koronis Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Koronis Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 13.8 µg/L. Always check local health department advisories before swimming.
How deep is Koronis Lake?
- Koronis Lake has a maximum depth of 132 feet and an average depth of 29 feet. The lake covers 2968.28 acres.
What fish are in Koronis Lake?
- Fish species found in Koronis Lake include bigmouth buffalo, black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, common carp, golden redhorse, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, river redhorse, rock bass, shorthead redhorse, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Koronis Lake is located in Stearns County, Minnesota.
When does Koronis Lake thaw?
- Koronis Lake typically has ice-out around Apr 14. Ice typically forms around Dec 1. The open water season is approximately 231 days.
Does Koronis Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Koronis Lake (clouds, ice, or an off-season gap). The most recent reading was moderate (33,113 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Koronis Lake?
- Koronis Lake has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Highway 55 Bridge, Koronis Lake County Park, Koronis Lake Park. Public access is listed as yes.
Explore Koronis 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 Stearns County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Crow River Watershed, ranked by water quality
Lakes in the Sauk River Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Koronis Lake
Other Grade C Lakes in Minnesota
Eutrophic Lakes in Minnesota
Compare Koronis Lake With Nearby Lakes
Where this data comes from
212 measurements from 3 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
MNPCA212 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 (3)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
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