Rock Lake
Rock Lake in Clearwater County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.2 ft visibility. Phosphorus: 16.5 µg/L. Chlorophyll-a (algae): 4.9 µg/L.
- Clarity
- 11.2 ft
- Typical in August
- 69°F
- Type
- Mesotrophic
- Trend
- ↓ Declining
- Public access
- Yes
Next lake in Clearwater County
Rock Lake is a mesotrophic lake in Clearwater County, Minnesota. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 36 other monitored lakes in Clearwater County, Rock Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-04. 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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Good clarity, visible to about 11.2 ft. Phosphorus level: 16.5 µg/L. Chlorophyll-a: 4.9 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.2 ft | Not graded |
| Phosphorus | 16.5 µg/L | Good |
| Chlorophyll-a (Algae) | 4.9 µg/L | Good |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Rock Lake
Compare lakeside cabins, hotels, and vacation rentals near Rock Lake in Clearwater 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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Water Temperature
Rock Lake typically sits around 69°F at the surface in August. Summer average is about 67°F. Usually warmest in Jul (about 69°F) and coldest in May (about 56°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 47 field readings (2016–2025) via the EPA Water Quality Portal. See the full Rock Lake water temperature breakdown →
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fishing Rock Lake
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Rock Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Aquatic Plant Report — Rock (1416)Aquatic Plant Report · 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 | ↑ Improving | +0.65 m/yr | 2 |
| Phosphorus | ↓ Declining | +3.5 µg/L/yr | 2 |
| Chlorophyll-a | ↓ Declining | +2.4 µg/L/yr | 2 |
County Ranking
Ranked #5 of 37 lakes in Clearwater County
Nearby Lakes in Clearwater County
Frequently asked questions about Rock Lake
What is the water quality grade for Rock Lake?
- Rock Lake in Clearwater County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.2 ft visibility. Phosphorus: 16.5 µg/L. Chlorophyll-a (algae): 4.9 µg/L.
Is Rock Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Rock Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 4.9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Rock Lake?
- Rock Lake typically sits around 69°F at the surface in August, from 47 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
How deep is Rock Lake?
- The available depth estimate for Rock Lake is shallower than its measured water clarity, which cannot be right, so no depth is shown.
Explore Rock Lake across LakeGrade
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Fish species and best lakes in Clearwater County
Species activity outlook by water temperature and season
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Moderate nutrients, good water quality
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State Parks Near Rock Lake
Other Grade A Lakes in Minnesota
Mesotrophic Lakes in Minnesota
Where this data comes from
34 measurements from 2 monitoring stations, 2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Chippewa Tribe, Minnesota (White Earth Band) (Tribal)
WEARTH_WQX34 samples · 2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity by Nephelometry
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
Lake size & watershed from HydroLAKES (HydroSHEDS)