Roy Lake
Roy Lake in Mahnomen County, Minnesota has a water quality grade of C (Fair). 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.
- Clarity
- 6 ft
- Typical in August
- 73°F
- Max depth
- 16 ft
- Area
- 695 acres
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 27
- Open water
- 196 days
Next lake in Mahnomen County
Roy Lake is a 695-acre productive, nutrient-rich eutrophic lake in Mahnomen County, Minnesota with a maximum depth of 16 feet. Water quality is graded C based on 2 sampling years through 2025. 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. Grade methodology: LakeGrade methodology.
Watch Roy Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Murky, only visible to about 6 ft. Phosphorus level: 24 µg/L. Chlorophyll-a: 13.6 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6 ft | Not graded |
| Phosphorus | 24 µg/L | Good |
| Chlorophyll-a (Algae) | 13.6 µg/L | Fair |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay 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
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 →
Water Temperature
Roy Lake typically sits around 73°F at the surface in August. 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.
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 ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 16 ft |
| Surface Area | 695 acres |
| Shoreline Length | 4.1 mi |
| Littoral Zone | 92% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Roy Lake
DNR Fisheries Survey Summary
10 surveys on file from MN DNR Fisheries. Most recent: 2023-07-17 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 43.21 | 0.12 lb |
| Brown Bullhead | 25.67 | 0.46 lb |
| Pumpkinseed | 20.34 | 0.13 lb |
| Yellow Bass | 16.21 | 0.54 lb |
| IOD | 11.87 | — |
| Largemouth Bass | 9.70 | 0.87 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
Brown Bullhead
Pumpkinseed
Yellow Bass
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
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.221 m/yr | 6 |
| Phosphorus | ↓ Declining | +4.25 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -4.3 µg/L/yr | 2 |
Ice Season
Historical ice data from Minnesota DNR (8 observations).
Estimated open water season: 196 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2004-04-14 (2004) | 2022-05-06 (2022) |
| Ice-In | 2017-11-06 (2017) | 2015-11-20 (2015) |
Most recent ice-out: 2022-05-06
County Ranking
Ranked #7 of 12 lakes in Mahnomen County
Nearby Lakes in Mahnomen County
Frequently asked questions about Roy Lake
What is the water quality grade for Roy Lake?
- Roy Lake in Mahnomen County, Minnesota has a water quality grade of C (Fair). 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?
- Generally safe for swimming, moderate water quality. Roy Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 13.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Roy Lake?
- Roy Lake typically sits around 73°F at the surface in August, 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.
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.
Explore Roy Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded 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 grade
Lakes in the Red River of the North Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Roy Lake
Other Grade C 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)
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)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate