What is the water quality grade for Grass Lake?

Grass Lake in Gladwin County, Michigan received a water quality grade of B (Good). Water clarity: 4 ft visibility. Chlorophyll-a (algae): 3.4 µg/L.

Is Grass Lake safe to swim in?

Good for swimming, clear water with low algae levels. Grass Lake has an overall water quality grade of B. Algae concentration (chlorophyll-a) is 3.4 µg/L. Always check local health department advisories before swimming.

Gladwin County, Michigan · 44.12°N

Grass Lake

Grade BGood · 4 ft clarity

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Mesotrophic

Grass Lake is a mesotrophic lake in Gladwin County, Michigan. Water quality is graded B based on 2 sampling years through 2023. Overall water quality is improving over recent sampling years. The lake supports 6 documented fish species including Bluntnose minnow, Fathead minnow, and Finescale dace. Compared to the 8 other monitored lakes in Gladwin County, Grass Lake ranks #5 for water quality.

Source: EPA Water Quality Portal sampling records, Michigan DNR, last sampled 2023-09-10. Grade methodology: LakeGrade methodology.

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Swimming Safety

Good for swimming, clear water with low algae levels

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Water Quality Grade: B, Good

Murky, only visible to about 4 ft. Chlorophyll-a: 3.4 µg/L. Trophic State Index: 50.

Metric	Value	Grade
Water Clarity (Secchi Depth)	4 ft	D
Phosphorus	No data
Chlorophyll-a (Algae)	3.4 µg/L	A
Trophic State Index (TSI)	50	Mesotrophic

Moderate nutrients, good water quality

Where to stay near Grass Lake

Compare lakeside cabins, hotels, and vacation rentals near Grass Lake in Gladwin County, Michigan — 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.

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Fish Species

Bluntnose minnow Fathead minnow Finescale dace Green sunfish Smallmouth bass Western banded killifish

Click a species to see every graded lake where it is documented.

Fishing Grass Lake

Water Quality Trend: ↑ Improving

Based on 3 years of monitoring data (2020-2025).

Metric	Trend	Change/Year	Years
Water Clarity	↑ Improving	+0.87 m/yr	3
Chlorophyll-a	↑ Improving	-0.8 µg/L/yr	2

Water Temperature

Grass Lake averages about 75°F at the surface in summer, usually warmest in Jun (about 77°F) and coldest in May (about 61°F). These are typical values by month — not a live reading.

Jan

—

Feb

—

Mar

—

Apr

—

May

61°

Jun

77°

Jul

77°

Aug

70°

Sep

70°

Oct

—

Nov

—

Dec

—

Typical surface water temperature by month, from 32 field readings (2023–2023) via the EPA Water Quality Portal. See the full Grass Lake water temperature breakdown →

Location & Depth Map

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Free interactive depth-contour map of Grass Lake, reaching a maximum surveyed depth of 8 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Michigan DNR.