Roy Lake
Mahnomen County, Minnesota695 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Roy Lake. Here is what has been measured.
- Eutrophic
- 16 ft max depth
- Public access
Roy Lake in Mahnomen County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 6 ft visibility. Phosphorus: 24 µg/L. Chlorophyll-a (algae): 13.6 µg/L. Maximum depth: 16 ft. Surface area: 695.44 acres.
Minnesota DNR's Targeted Survey on July 17, 2023 caught 53.71 largemouth bass per hour of electrofishing at Roy Lake. Length samples in the latest survey that recorded them ran 5–17 inches. DNR survey details →
Roy Lake is a 695-acre productive, nutrient-rich eutrophic lake in Mahnomen County, Minnesota with a maximum depth of 16 feet. Overall water quality is improving over recent sampling years. The lake supports 13 documented fish species including black crappie, bluegill, and brown bullhead. Public access is available. Compared to the 11 other monitored lakes in Mahnomen County, Roy Lake ranks #7 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-30. Methodology: how these readings are compared.
Roy Lake covers about 700 acres in Mahnomen County. The median ice-out date is April 27, which is when the open-water season begins. If you are planning to stay, you can search lake houses and cabins around Roy Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What Roy Lake is good for
From access and monitoring records, not editorial picks.
- Fishing13 species recorded
- Ice seasonIce-out around Apr 27
Swimming conditions
Readings onlyModerate 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 Roy 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 Roy Lake
These are the measurements Minnesota PCA publishes for Roy Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 6 ft. Phosphorus 24 µg/L. Chlorophyll-a 13.6 µg/L. TSI 52.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 24µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 13.6µg/L | Fair GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 52 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Roy Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Roy Lake typically sits around 66°F at the surface in September. Summer average is about 74°F. Usually warmest in Jul (about 77°F) and coldest in Sep (about 66°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (66°F) to its warmest (77°F).
Typical surface water temperature by month, from 60 field readings (2016–2025) via the EPA Water Quality Portal. See the full Roy Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Roy Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (301,995 cells/mL) on August 10, 2024.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Minnesota DNR's Targeted Survey on July 17, 2023 caught 53.71 largemouth bass per hour of electrofishing at Roy Lake. Length samples in the latest survey that recorded them ran 5–17 inches.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Roy 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
10 surveys on file from MN DNR Fisheries. Most recent: 2023-07-17 (Targeted Survey).
10 surveys on file · most recent 2023-07-17 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluegill | 43.21 | 3–7 in 2022-07-18 | 0.12 lb |
| Brown Bullhead | 25.67 | 8–13 in 2022-07-18 | 0.46 lb |
| Pumpkinseed | 20.34 | 3–7 in 2022-07-18 | 0.13 lb |
| Yellow Bullhead | 16.21 | 7–13 in 2022-07-18 | 0.54 lb |
| Largemouth Bass | 9.70 | 5–17 in 2022-07-18 | 0.87 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.
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
Brown Bullhead
Pumpkinseed
Yellow Bullhead
From the 2023-07-17 survey
A targeted survey of nearshore fish species in Roy Lake, which lies within the boundaries of the White Earth Reservation, was conducted on July 17-18, 2023 by Index of Biological Integrity (IBI) Program Staff. Sampling sites were evenly spaced around the lake and each was sampled by backpack electrofishing and seining…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Roy Lake. 5 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — RoyFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Roy (1694)Aquatic Plant Report · MN DNR LakeFinder
- —Aquatic Plant Report — Roy (1947)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — RoyFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — RoyPublic Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
16 ft
Surface area
695 acres
Shoreline
4.1 mi
Littoral zone
92%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
5 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,480 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near Roy Lake
Compare lakeside cabins, hotels, and vacation rentals near Roy Lake in Mahnomen 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 Roy Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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Fish Species
Click a species to see every lake where it is documented.
Fishing Roy Lake
Water Quality Trend: Improving
Based on 6 years of monitoring (2020–2025).
Water clarity
Improving6 years
Phosphorus
Worsening+4.25 µg/L/yr2 years
Chlorophyll-a
Improving-4.3 µg/L/yr2 years
Ice season
Typical ice-out
Apr 27
Earliest Apr 14, 2004 · Latest May 6, 2022
Typical ice-in
Nov 9
Earliest Nov 6, 2017 · Latest Nov 20, 2015
Most recent ice-out
May 6
2022
8 observations · Minnesota PCA ice records
Nearby Lakes in Mahnomen County
Frequently asked questions about Roy Lake
Where is Roy Lake?
- Roy Lake is a lake in Mahnomen County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Roy Lake?
- Roy Lake in Mahnomen County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 6 ft visibility. Phosphorus: 24 µg/L. Chlorophyll-a (algae): 13.6 µg/L. Maximum depth: 16 ft. Surface area: 695.44 acres.
Is Roy 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 Roy Lake?
- Roy Lake typically sits around 66°F at the surface in September, from 60 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
How deep is Roy Lake?
- Roy Lake has a maximum depth of 16 feet. The lake covers 695.44 acres.
What fish are in Roy Lake?
- Fish species found in Roy Lake include black crappie, bluegill, brown bullhead, common carp, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, white sucker, yellow bullhead, yellow perch. Roy Lake is located in Mahnomen County, Minnesota.
What did the DNR fisheries survey find at Roy Lake?
- Minnesota DNR's Targeted Survey on July 17, 2023 caught 53.71 largemouth bass per hour of electrofishing at Roy Lake. Length samples in the latest survey that recorded them ran 5–17 inches. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Roy 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 Roy Lake thaw?
- Roy Lake typically has ice-out around Apr 27. Ice typically forms around Nov 9. The open water season is approximately 196 days.
Does Roy Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Roy Lake (clouds, ice, or an off-season gap). The most recent reading was high (301,995 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Can I fish at Roy Lake?
- Public access to Roy Lake is listed as yes on the lake record. 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.
Explore Roy Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Fish species and the cleanest lakes across Minnesota
Fish species and best lakes in Mahnomen County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its readings
Lakes in the Red River of the North Watershed, ranked by water quality
Minnesota's cleanest lakes, ranked on agency measurements
More lakes in Minnesota
State Parks Near Roy Lake
Other Lakes in Minnesota
Eutrophic Lakes in Minnesota
Compare Roy Lake With Nearby Lakes
Where this data comes from
130 measurements from 3 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
MNPCA102 samples · 2020–2025 - Minnesota Chippewa Tribe, Minnesota (White Earth Band) (Tribal)
WEARTH_WQX28 samples · 2023
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 (3)
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