Rock Lake
Rock Lake in Crow Wing County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 7.4 ft visibility. Phosphorus: 18 µg/L. Chlorophyll-a (algae): 6.3 µg/L. Maximum depth: 22 ft. Surface area: 203.41 acres.
- Clarity
- 7.4 ft
- Typical in August
- 73°F
- Max depth
- 22 ft
- Area
- 203 acres
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 10
Next lake in Crow Wing County
Why Rock 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 Rock Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. 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.
Rock Lake is a 203-acre lake in Crow Wing County, Minnesota with a maximum depth of 22 feet. Overall water quality is improving over recent sampling years. The lake supports 17 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 3 public boat landings.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-08-09. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Rock Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Moderate clarity, visible to about 7.4 ft. Phosphorus level: 18 µg/L. Chlorophyll-a: 6.3 µg/L. Trophic State Index: 48.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7.4 ft | Not graded |
| Phosphorus | 18 µg/L | Not graded |
| Chlorophyll-a (Algae) | 6.3 µg/L | Not graded |
| Trophic State Index (TSI) | 48 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Rock Lake
Compare lakeside cabins, hotels, and vacation rentals near Rock Lake in Crow Wing 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 Rock Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Rock Lake typically sits around 73°F at the surface in August. Summer average is about 72°F. Usually warmest in Jul (about 74°F) and coldest in May (about 60°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 38 field readings (2016–2024) via the EPA Water Quality Portal. See the full Rock Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 22 ft |
| Surface Area | 203 acres |
| Shoreline Length | 3.7 mi |
| Littoral Zone | 63% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Long LakePublic
- Erskine LakePublic
- Rock LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Rock Lake
DNR Fisheries Survey Summary
2 surveys on file from MN DNR Fisheries. Most recent: 2022-07-20 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Green Sunfish | 97.83 | — |
| Largemouth Bass | 19.46 | 0.34 lb |
| Bluegill | 15.25 | 0.12 lb |
| Yellow Perch | 15.22 | 0.07 lb |
| Bluntnose Minnow | 12.37 | — |
| Hybrid Sunfish | 8.34 | 0.18 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.
Largemouth Bass
Bluegill
Yellow Perch
Hybrid Sunfish
From the 2022-07-20 survey
Rock Lake is a 203 acre lake, with a maximum depth of 22', located three miles south of Pine Center in Crow Wing County. Rock is in the Mississippi River-Sartell watershed. A nearshore survey was conducted to assess the populations of both game and non-game fish species. Ten 100' long sampling stations were evenly…
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 (0209)Aquatic Plant Report · MN DNR LakeFinder
- —Aquatic Plant Report — Rock (2036)Aquatic Plant Report · MN DNR LakeFinder
- —Public Water Access Sites — RockPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.327 m/yr | 4 |
Ice Season
Historical ice data from Minnesota DNR (10 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-03-11 (2024) | 2022-05-10 (2022) |
| Ice-In | 2021-11-28 (2021) | 2021-11-28 (2021) |
Most recent ice-out: 2024-03-11
EPA Impairment Status
Rock 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 MN18-0088-00 · Official waterbody report · Matched by proximity (2.46 km)
Graded lakes near Rock Lake
Rock Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Crow Wing County
Frequently asked questions about Rock Lake
What is the water quality grade for Rock Lake?
- Rock Lake in Crow Wing County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 7.4 ft visibility. Phosphorus: 18 µg/L. Chlorophyll-a (algae): 6.3 µg/L. Maximum depth: 22 ft. Surface area: 203.41 acres.
Is Rock Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Rock Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Algae concentration (chlorophyll-a) is 6.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Rock Lake?
- Rock Lake typically sits around 73°F at the surface in August, from 38 EPA Water Quality Portal field readings (2016–2024). That is a typical value for the month, not a live reading.
How deep is Rock Lake?
- Rock Lake has a maximum depth of 22 feet. The lake covers 203.41 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, rock bass, sunfish, walleye, white sucker, yellow bullhead, yellow perch. Rock Lake is located in Crow Wing County, Minnesota.
When does Rock Lake thaw?
- Rock Lake typically has ice-out around Apr 10.
Are there boat ramps on Rock Lake?
- Rock Lake has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Long Lake, Erskine Lake, Rock Lake. Public access is listed as yes.
Explore Rock Lake across LakeGrade
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Where this data comes from
19 measurements from 2 monitoring stations, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA19 samples · 2020–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 2130 B ~ Nephelometric Method
- 2120 B ~ Color in Water by Visual Comparison
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
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