Mountain Lake
Mountain Lake in Cottonwood County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 1.2 ft visibility. Phosphorus: 123.5 µg/L. Chlorophyll-a (algae): 33.3 µg/L. Maximum depth: 8 ft. Surface area: 229.52 acres.
- Clarity
- 1.2 ft
- Typical in August
- 78°F
- Max depth
- 8 ft
- Area
- 230 acres
- Type
- Hypereutrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Mar 30
- Open water
- 247 days
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Mountain Lake →
Next lake in Cottonwood County
Mountain Lake is a 230-acre highly nutrient-loaded hypereutrophic lake in Cottonwood County, Minnesota with a maximum depth of 8 feet. Water quality is graded F based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. The lake supports 12 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 2 public boat landings. Compared to the 2 other monitored lakes in Cottonwood County, Mountain Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-03. Grade methodology: LakeGrade methodology.
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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 1.2 ft of visibility. Phosphorus level: 123.5 µg/L. Chlorophyll-a: 33.3 µg/L. Trophic State Index: 71.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.2 ft | Not graded |
| Phosphorus | 123.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 33.3 µg/L | Poor |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Mountain Lake
Compare lakeside cabins, hotels, and vacation rentals near Mountain Lake in Cottonwood 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 Mountain Lake are listed below.
Top-rated places to stay near Mountain 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
Mountain Lake typically sits around 78°F at the surface in August. Summer average is about 76°F. Usually warmest in Jul (about 79°F) and coldest in Jun (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 25 field readings (2024–2025) via the EPA Water Quality Portal. See the full Mountain Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 8 ft |
| Surface Area | 230 acres |
| Shoreline Length | 4.2 mi |
| Littoral Zone | 96% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Mountain Lake (West)Public
- Mountain Lake (East)Public
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Mountain Lake
DNR Fisheries Survey Summary
12 surveys on file from MN DNR Fisheries. Most recent: 2025-05-06 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 62.31 | 0.36 lb |
| Largemouth Bass | 36.34 | 1.11 lb |
| Bluegill | 33.01 | 0.17 lb |
| YLB | 29.72 | — |
| Yellow Perch | 27.15 | 0.19 lb |
| White Crappie | 25.44 | 0.31 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.
Black Bullhead
Largemouth Bass
Bluegill
YLB
From the 2025-05-06 survey
Mountain Lake is a 241-acre, class 43 lake, located within the City of Mountain Lake in Cottonwood County. The lake has a maximum depth of 7.0 feet, and has a watershed-to-lake ratio of 22-to-1. In the early 1990's, Mountain Lake had a diverse population of fish. During the winter of 1993-94, the lake suffered a…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Mountain Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — MountainFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — MountainFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — MountainPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.08 m/yr | 2 |
| Phosphorus | ↑ Improving | -35.5 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -13.2 µg/L/yr | 2 |
Ice Season
Historical ice data from Minnesota DNR (15 observations).
Estimated open water season: 247 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2016-03-15 (2016) | 2018-04-29 (2018) |
| Ice-In | 2018-11-09 (2018) | 2004-12-19 (2004) |
Most recent ice-out: 2020-03-29
Reservoir Info (USACE NID)
Mountain Lake is a man-made reservoir impounded by the Mountain Lake (completed 1960), built primarily for recreation on the Blue Earth River-TR; other-type dam, 15 ft tall and 25 ft long.
- Surface area
- 230 ac
- Normal storage
- 1,145 ac-ft
- Max storage
- 1,832 ac-ft
- Drainage area
- 9.9 sq mi
- Hazard class
- Significant
- Owner
- MNDNR
Source: USACE National Inventory of Dams, NID ID MN00165 · Operator website
EPA Impairment Status
Mountain 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 MN17-0003-00 · Official waterbody report
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Mountain Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Mountain Lake WwtpMountain Lake · 0.9 mi away · NPDES MN0021466Recent violation
- Mountain Lake WtpMountain Lake · 1.2 mi away · NPDES MN0002763
- Milk Specialties IncMountain Lake · 2 mi away · NPDES MN0066036
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 #3 of 3 lakes in Cottonwood County
Nearby Lakes With Higher Grades
Mountain Lake holds Grade F. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Cottonwood County
Frequently asked questions about Mountain Lake
What is the water quality grade for Mountain Lake?
- Mountain Lake in Cottonwood County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 1.2 ft visibility. Phosphorus: 123.5 µg/L. Chlorophyll-a (algae): 33.3 µg/L. Maximum depth: 8 ft. Surface area: 229.52 acres.
Is Mountain 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. Mountain Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 33.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Mountain Lake?
- Mountain Lake typically sits around 78°F at the surface in August, from 25 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Mountain Lake?
- Mountain Lake has a maximum depth of 8 feet. The lake covers 229.52 acres.
What fish are in Mountain Lake?
- Fish species found in Mountain Lake include black bullhead, black crappie, bluegill, common carp, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, yellow bass, yellow bullhead, yellow perch. Mountain Lake is located in Cottonwood County, Minnesota.
When does Mountain Lake thaw?
- Mountain Lake typically has ice-out around Mar 30. Ice typically forms around Dec 2. The open water season is approximately 247 days.
Are there boat ramps on Mountain Lake?
- Mountain Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Mountain Lake (West), Mountain Lake (East). Public access is listed as yes.
Explore Mountain Lake across LakeGrade
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Species activity outlook by water temperature and season
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Very high nutrients, dense algae, poor clarity
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Where this data comes from
24 measurements from 1 monitoring station, 2024–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA24 samples · 2024–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
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