Rock Lake
Rock Lake in Wright County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 2.6 ft visibility. Phosphorus: 64 µg/L. Chlorophyll-a (algae): 59.6 µg/L. Maximum depth: 37 ft. Surface area: 183.12 acres.
- Clarity
- 2.6 ft
- Max depth
- 37 ft
- Area
- 183 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 5
- Open water
- 245 days
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Rock Lake →
Next lake in Wright County
Rock Lake is a 183-acre productive, nutrient-rich eutrophic lake in Wright County, Minnesota with a maximum depth of 37 feet (14-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 15 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 50 other monitored lakes in Wright County, Rock Lake ranks #33 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-14. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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 2.6 ft of visibility. Phosphorus level: 64 µg/L. Chlorophyll-a: 59.6 µg/L. Trophic State Index: 66.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.6 ft | Not graded |
| Phosphorus | 64 µg/L | Poor |
| Chlorophyll-a (Algae) | 59.6 µg/L | Poor |
| Trophic State Index (TSI) | 66 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Rock Lake
Compare lakeside cabins, hotels, and vacation rentals near Rock Lake in Wright 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 Rock Lake are listed below.
Top-rated places to stay near Rock 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 | 37 ft |
| Average Depth | 13.6 ft |
| Surface Area | 183 acres |
| Shoreline Length | 3 mi |
| Littoral Zone | 54% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Rock LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing 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
8 surveys on file from MN DNR Fisheries. Most recent: 2025-08-11 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 101.97 | 0.2 lb |
| Green Sunfish | 34.91 | 0.19 lb |
| Largemouth Bass | 17.91 | 0.83 lb |
| GOS | 14.27 | 0.09 lb |
| Black Crappie | 12.61 | 0.35 lb |
| Yellow Bass | 7.97 | 0.75 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.
Bluegill
Green Sunfish
Largemouth Bass
GOS
From the 2025-08-11 survey
A targeted survey of nearshore fish species in Rock Lake, was conducted on August 11th, 2025, by Area Fisheries staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible. Backpack electrofishing was completed at…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for 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 — RockFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Rock (2017)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — RockFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — RockPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.338 m/yr | 2 |
Ice Season
Historical ice data from Minnesota DNR (8 observations).
Estimated open water season: 245 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2003-03-30 (2003) | 2002-04-15 (2002) |
| Ice-In | 2003-11-22 (2003) | 2001-12-08 (2001) |
Most recent ice-out: 2005-04-06
EPA Impairment Status
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 MN86-0182-00 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Rock Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 1 facility has a reported Clean Water Act violation in the past three years.
- Annandale/Maple Lake/Howard Lake WwtpMaple Lake · 1.2 mi away · NPDES MN0066966MajorRecent violation
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 #33 of 51 lakes in Wright County
Nearby Lakes With Higher Grades
Rock 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.
Nearby Lakes in Wright County
Frequently asked questions about Rock Lake
What is the water quality grade for Rock Lake?
- Rock Lake in Wright County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 2.6 ft visibility. Phosphorus: 64 µg/L. Chlorophyll-a (algae): 59.6 µg/L. Maximum depth: 37 ft. Surface area: 183.12 acres.
Is 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. Rock Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 59.6 µg/L. Always check local health department advisories before swimming.
How deep is Rock Lake?
- Rock Lake has a maximum depth of 37 feet and an average depth of 13.6 feet. The lake covers 183.12 acres.
What fish are in Rock Lake?
- Fish species found in Rock Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, common carp, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, white crappie, yellow bullhead, yellow perch. Rock Lake is located in Wright County, Minnesota.
When does Rock Lake thaw?
- Rock Lake typically has ice-out around Apr 5. Ice typically forms around Dec 6. The open water season is approximately 245 days.
Are there boat ramps on Rock Lake?
- Rock Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Rock Lake. Public access is listed as yes.
Explore Rock Lake across LakeGrade
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Species activity outlook by water temperature and season
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High nutrients, frequent algae, reduced clarity
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Where this data comes from
23 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA23 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 (2)
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