Lost Lake
Lost Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 14.8 ft visibility. Phosphorus: 10.5 µg/L. Chlorophyll-a (algae): 2.3 µg/L. Maximum depth: 26 ft. Surface area: 68.5 acres.
- Clarity
- 14.8 ft
- Typical in August
- 73°F
- Max depth
- 26 ft
- Area
- 69 acres
- Type
- Oligotrophic
- Trend
- → Stable
- Public access
- No
- Ice-out
- Apr 15
- Open water
- 219 days
Next lake in Cass County
Lost Lake is a 69-acre cold, clear oligotrophic lake in Cass County, Minnesota with a maximum depth of 26 feet. Water quality is graded A based on 2 sampling years through 2025. Water clarity is improving over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 103 other monitored lakes in Cass County, Lost Lake ranks #50 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-29. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Good clarity, visible to about 14.8 ft. Phosphorus level: 10.5 µg/L. Chlorophyll-a: 2.3 µg/L. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 14.8 ft | Not graded |
| Phosphorus | 10.5 µg/L | Good |
| Chlorophyll-a (Algae) | 2.3 µg/L | Good |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Lost Lake
Compare lakeside cabins, hotels, and vacation rentals near Lost Lake in Cass 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 Lost Lake
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Water Temperature
Lost Lake typically sits around 73°F at the surface in August. Summer average is about 74°F. Usually warmest in Jul (about 78°F) and coldest in May (about 63°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 51 field readings (2011–2024) via the EPA Water Quality Portal. See the full Lost Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 26 ft |
| Surface Area | 69 acres |
| Shoreline Length | 2.5 mi |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fishing Lost Lake
DNR Fisheries Survey Summary
1 survey on file from MN DNR Fisheries. Most recent: 1990-07-12 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 12.63 | 0.2 lb |
| Black Bullhead | 9.50 | 0.6 lb |
| Northern Pike | 7.00 | 1.05 lb |
| Yellow Bass | 4.13 | 0.35 lb |
| Rock Bass | 2.25 | 0.33 lb |
| Pumpkinseed | 1.50 | 0.15 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
From the 1990-07-12 survey
The northern pike gillnet catch of 13.5 is high. Most of the fish sampled were less than 20 inches long, but fish 30 inches long were collected. The northern pike growth rate is near the statewide average.The bluegill trapnet catch was 23.8. The sample collected exhibited fair quality indices - PSD=54; RSD-7=19;…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Lost Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — LostFisheries Lake Survey · MN DNR LakeFinder
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.125 m/yr | 6 |
| Phosphorus | → Stable | +0.07 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.17 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (20 observations).
Estimated open water season: 219 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2016-03-31 (2016) | 2008-04-30 (2008) |
| Ice-In | 2017-11-10 (2017) | 2007-11-27 (2007) |
Most recent ice-out: 2017-04-04
EPA Impairment Status
Lost 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 MN11-0270-00 · Official waterbody report · Matched by proximity (1.31 km)
County Ranking
Ranked #50 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Lost Lake
What is the water quality grade for Lost Lake?
- Lost Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 14.8 ft visibility. Phosphorus: 10.5 µg/L. Chlorophyll-a (algae): 2.3 µg/L. Maximum depth: 26 ft. Surface area: 68.5 acres.
Is Lost Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Lost Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Lost Lake?
- Lost Lake typically sits around 73°F at the surface in August, from 51 EPA Water Quality Portal field readings (2011–2024). That is a typical value for the month, not a live reading.
How deep is Lost Lake?
- Lost Lake has a maximum depth of 26 feet. The lake covers 68.5 acres.
When does Lost Lake thaw?
- Lost Lake typically has ice-out around Apr 15. Ice typically forms around Nov 20. The open water season is approximately 219 days.
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Where this data comes from
110 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA110 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 (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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate