Red Rock Lake
Red Rock Lake in Douglas County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3.6 ft visibility. Phosphorus: 55 µg/L. Chlorophyll-a (algae): 33.7 µg/L. Maximum depth: 22 ft. Surface area: 904.1 acres.
- Clarity
- 3.6 ft
- Typical in August
- 75°F
- Max depth
- 22 ft
- Area
- 904 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 7
- Open water
- 231 days
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Red Rock Lake →
Next lake in Douglas County
Free interactive depth-contour map of Red Rock Lake, reaching a maximum surveyed depth of 20 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Red Rock Lake is a 904-acre productive, nutrient-rich eutrophic lake in Douglas County, Minnesota with a maximum depth of 22 feet (9-foot average). Water quality is graded F based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 13 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 36 other monitored lakes in Douglas County, Red Rock Lake ranks #34 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-22. 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)
Murky, only visible to about 3.6 ft. Phosphorus level: 55 µg/L. Chlorophyll-a: 33.7 µg/L. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.6 ft | Not graded |
| Phosphorus | 55 µg/L | Poor |
| Chlorophyll-a (Algae) | 33.7 µg/L | Poor |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Red Rock Lake
Compare lakeside cabins, hotels, and vacation rentals near Red Rock Lake in Douglas 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 Red Rock Lake are listed below.
Top-rated places to stay near Red Rock Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Red Rock Lake typically sits around 75°F at the surface in August. Summer average is about 73°F. Usually warmest in Jul (about 76°F) and coldest in May (about 59°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 41 field readings (2011–2021) via the EPA Water Quality Portal. See the full Red Rock Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Red Rock Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (54,450 cells/mL) on November 22, 2025.
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 | 22 ft |
| Average Depth | 9.1 ft |
| Surface Area | 904 acres |
| Shoreline Length | 11.7 mi |
| Littoral Zone | 57% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Red Rock LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Red Rock 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
15 surveys on file from MN DNR Fisheries. Most recent: 2025-06-02 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 24.00 | 0.7 lb |
| Yellow Perch | 20.33 | 0.22 lb |
| Largemouth Bass | 16.41 | 1.18 lb |
| Fathead Minnow | 15.24 | — |
| Black Crappie | 11.06 | 0.25 lb |
| Bluegill | 8.82 | 0.32 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
Yellow Perch
Largemouth Bass
Black Crappie
From the 2025-06-02 survey
Red Rock Lake is a 902-acre shallow lake located approximately seven miles northeast of Hoffman. Maximum depth is 22 feet. Average depth is estimated at 9 feet. Water transparency has improved over time, averaging over 10 feet during early summer months since 2010. A trend in increasing water clarity is expected to…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Red Rock Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — Red RockFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Red Rock (0927)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — Red RockFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — Red RockPublic 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 | -0.023 m/yr | 6 |
| Phosphorus | ↓ Declining | +4.99 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +8.81 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (37 observations).
Estimated open water season: 231 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-03-13 (2024) | 2008-04-24 (2008) |
| Ice-In | 1991-11-04 (1991) | 2001-12-12 (2001) |
Most recent ice-out: 2024-03-13
EPA Impairment Status
Red Rock 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 MN21-0291-00 · Official waterbody report
County Ranking
Ranked #34 of 37 lakes in Douglas County
Nearby Lakes in Douglas County
Frequently asked questions about Red Rock Lake
What is the water quality grade for Red Rock Lake?
- Red Rock Lake in Douglas County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3.6 ft visibility. Phosphorus: 55 µg/L. Chlorophyll-a (algae): 33.7 µg/L. Maximum depth: 22 ft. Surface area: 904.1 acres.
Is Red Rock 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. Red Rock Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 33.7 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Red Rock Lake?
- Red Rock Lake typically sits around 75°F at the surface in August, from 41 EPA Water Quality Portal field readings (2011–2021). That is a typical value for the month, not a live reading.
How deep is Red Rock Lake?
- Red Rock Lake has a maximum depth of 22 feet and an average depth of 9.1 feet. The lake covers 904.1 acres.
What fish are in Red Rock Lake?
- Fish species found in Red Rock Lake include black bullhead, black crappie, bluegill, brown bullhead, common carp, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, yellow bullhead, yellow perch. Red Rock Lake is located in Douglas County, Minnesota.
When does Red Rock Lake thaw?
- Red Rock Lake typically has ice-out around Apr 7. Ice typically forms around Nov 24. The open water season is approximately 231 days.
Does Red Rock Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Red Rock Lake (clouds, ice, or an off-season gap). The most recent reading was moderate (54,450 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Red Rock Lake?
- Red Rock Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Red Rock Lake. Public access is listed as yes.
Explore Red Rock Lake across LakeGrade
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Where this data comes from
84 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
MNPCA84 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
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate