Mule Lake
Mule Lake in Otter Tail County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 17.1 ft visibility. Phosphorus: 8 µg/L. Chlorophyll-a (algae): 1.3 µg/L. Maximum depth: 31 ft. Surface area: 53.36 acres.
- Clarity
- 17.1 ft
- Max depth
- 31 ft
- Area
- 53 acres
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Otter Tail County
Why Mule Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Mule Lake, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded water clarity, phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by MPCA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Mule Lake is a 53-acre lake in Otter Tail County, Minnesota with a maximum depth of 31 feet. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-08-02. Grade methodology: LakeGrade methodology.
Watch Mule Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Mule Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Crystal clear, you can see 17.1 ft down. Phosphorus level: 8 µg/L. Chlorophyll-a: 1.3 µg/L. Trophic State Index: 35.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 17.1 ft | Not graded |
| Phosphorus | 8 µg/L | Not graded |
| Chlorophyll-a (Algae) | 1.3 µg/L | Not graded |
| Trophic State Index (TSI) | 35 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Mule Lake
Compare lakeside cabins, hotels, and vacation rentals near Mule Lake in Otter Tail 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 Mule 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 31 ft |
| Surface Area | 53 acres |
| Shoreline Length | 2.3 mi |
| Littoral Zone | 64% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Heilberger LakePublic
Fishing Mule Lake
DNR Fisheries Survey Summary
1 survey on file from MN DNR Fisheries. Most recent: 1992-06-22 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 63.63 | 0.17 lb |
| Yellow Bass | 11.25 | 0.2 lb |
| Brown Bullhead | 9.25 | 0.27 lb |
| Black Crappie | 7.25 | 0.3 lb |
| Pumpkinseed | 5.75 | 0.1 lb |
| Hybrid Sunfish | 3.50 | 0.37 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
From the 1992-06-22 survey
Mule Lake is included in class 33 of the MN DNR lake classification system. Other area lakes in this class include: Anderson, Belmont, Jim, and Tonseth. Northern pike abundance is below normal for this lake class with a gill net catch rate of 1.0 per lift. The average weight of individual northern pike was 2.9 pounds.…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Mule Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — MuleFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — MuleFish Stocking History · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.109 m/yr | 6 |
Graded lakes near Mule Lake
Mule Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Otter Tail County
Frequently asked questions about Mule Lake
What is the water quality grade for Mule Lake?
- Mule Lake in Otter Tail County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 17.1 ft visibility. Phosphorus: 8 µg/L. Chlorophyll-a (algae): 1.3 µg/L. Maximum depth: 31 ft. Surface area: 53.36 acres.
Is Mule Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Mule Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Algae concentration (chlorophyll-a) is 1.3 µg/L. Always check local health department advisories before swimming.
How deep is Mule Lake?
- Mule Lake has a maximum depth of 31 feet. The lake covers 53.36 acres.
Are there boat ramps on Mule Lake?
- Mule Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Heilberger Lake. Public access is listed as yes.
Explore Mule Lake across LakeGrade
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Otter Tail County
Species activity outlook by water temperature and season
Top lakes and where to stay in the Alexandria Lakes area
Top lakes and where to stay in the Detroit Lakes Area area
Top lakes and where to stay in the Otter Tail County area
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Red River of the North Watershed, ranked by water quality
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Mule Lake
Other Lakes in Minnesota
Oligotrophic Lakes in Minnesota
Where this data comes from
4 measurements from 1 monitoring station, 2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA4 samples · 2023
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 2120 B ~ Color in Water by Visual Comparison
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory