Rainy Lake
Cass County, Minnesota129 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Rainy Lake. Here is what has been measured.
- Oligotrophic
- 29 ft max depth
Rainy Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 13.9 ft visibility. Phosphorus: 11.5 µg/L. Chlorophyll-a (algae): 1.8 µg/L. Maximum depth: 29 ft. Surface area: 129.39 acres.
Minnesota DNR's Standard Survey on July 7, 1987 caught 1.25 walleye per gill net at Rainy Lake. DNR survey details →
Rainy Lake is a 129-acre cold, clear oligotrophic lake in Cass County, Minnesota with a maximum depth of 29 feet. Overall water quality 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, Rainy Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-12. Methodology: how these readings are compared.
What Rainy Lake is good for
From access and monitoring records, not editorial picks.
- Clear water13.9 ft of visibility
- Ice seasonIce-out around Apr 15
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Rainy Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Rainy Lake
These are the measurements Minnesota PCA publishes for Rainy Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 13.9 ft. Phosphorus 11.5 µg/L. Chlorophyll-a 1.8 µg/L. TSI 38.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 13.9ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 11.5µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 1.8µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 38 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Rainy Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Rainy Lake typically sits around 68°F at the surface in September. Summer average is about 66°F. Usually warmest in Aug (about 69°F) and coldest in May (about 52°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (52°F) to its warmest (69°F).
Typical surface water temperature by month, from 90 field readings (2023–2024) via the EPA Water Quality Portal. See the full Rainy Lake water temperature breakdown →
Minnesota DNR's Standard Survey on July 7, 1987 caught 1.25 walleye per gill net at Rainy Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Rainy Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
3 surveys on file from MN DNR Fisheries. Most recent: 1987-07-07 (Standard Survey).
3 surveys on file · most recent 1987-07-07 (Standard Survey)
39 years old| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluegill | 37.75 | 0.13 lb | |
| Yellow Perch | 6.09 | 0.11 lb | |
| Pumpkinseed | 5.84 | 0.22 lb | |
| Yellow Bullhead | 4.46 | 0.49 lb | |
| Black Crappie | 3.33 | 0.3 lb | |
| Northern Pike | 2.56 | 3.3 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
From the 1987-07-07 survey
The fish population does not seem to have changed appreciably since the lake survey done in 1962. The bulk of the fish biomass is still predominantly centrarchids, with bluegills, black crappies, and largemouth bass being the most sought-after fish by sportsmen. Looking at the age and growth data, it can be seen that…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Rainy Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — RainyFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Rainy (1579)Aquatic Plant Report · MN DNR LakeFinder
Lake Details
Max depth
29 ft
Surface area
129 acres
Shoreline
2.8 mi
Littoral zone
72%
Share shallower than 15 ft
Public access
No
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
1 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,322 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near Rainy Lake
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Top-rated places to stay near Rainy Lake
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Follow Rainy Lake’s readings
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Fishing Rainy Lake
Water Quality Trend: Improving
Based on 6 years of monitoring (2020–2025).
Water clarity
Worsening6 years
Phosphorus
Improving-1.79 µg/L/yr6 years
Chlorophyll-a
Improving-0.95 µg/L/yr6 years
Ice season
Typical ice-out
Apr 15
Earliest Mar 30, 2016 · Latest May 3, 1996
Typical ice-in
Nov 21
Earliest Nov 6, 1993 · Latest Dec 8, 1998
Most recent ice-out
May 1
2023
51 observations · Minnesota PCA ice records
Nearby Lakes in Cass County
Frequently asked questions about Rainy Lake
Where is Rainy Lake?
- Rainy Lake is a lake in Cass County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Rainy Lake?
- Rainy Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 13.9 ft visibility. Phosphorus: 11.5 µg/L. Chlorophyll-a (algae): 1.8 µg/L. Maximum depth: 29 ft. Surface area: 129.39 acres.
Is Rainy Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Rainy Lake?
- Rainy Lake typically sits around 68°F at the surface in September, from 90 EPA Water Quality Portal field readings (2023–2024). That is a typical value for the month, not a live reading.
How deep is Rainy Lake?
- Rainy Lake has a maximum depth of 29 feet. The lake covers 129.39 acres.
What did the DNR fisheries survey find at Rainy Lake?
- Minnesota DNR's Standard Survey on July 7, 1987 caught 1.25 walleye per gill net at Rainy Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Rainy Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
When does Rainy Lake thaw?
- Rainy Lake typically has ice-out around Apr 15. Ice typically forms around Nov 21. The open water season is approximately 220 days.
Can I fish at Rainy Lake?
- Public access to Rainy Lake is listed as no on the lake record, so confirm before you make the trip. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
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Where this data comes from
37 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA37 samples · 2020–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate