Gratiot Lake
Keweenaw County, Michigan1,453 acresView mapDirections
EGLE publishes the water-quality measurements for Gratiot Lake. Here is what has been measured.
- Oligotrophic
- 70 ft max depth
- Limited data
Gratiot Lake in Keweenaw County, Michigan has water-quality measurements published by EGLE, shown here as reported. Water clarity: 17 ft visibility. Phosphorus: 9 µg/L. Maximum depth: 70 ft. Surface area: 1453.1 acres.
Gratiot Lake is a 1,453-acre cold, clear oligotrophic lake in Keweenaw County, Michigan with a maximum depth of 70 feet. Water clarity is improving over recent sampling years. The lake supports 1 documented fish species including Ninespine stickleback. Compared to the 10 other monitored lakes in Keweenaw County, Gratiot Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, EGLE, last sampled 2023-09-14. Methodology: how these readings are compared.
Gratiot Lake covers about 1,500 acres in Keweenaw County. If you are planning to stay, you can search lake houses and cabins around Gratiot Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What Gratiot Lake is good for
From access and monitoring records, not editorial picks.
- Clear water17 ft of visibility
- Deep water70 ft surveyed max depth
- Big water1,453 acres
Swimming conditions
Readings onlyLimited data
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 Gratiot Lake is safe to swim in today is a call for the Michigan Department of Environment, Great Lakes, and Energy (EGLE) and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Gratiot Lake
These are the measurements EGLE publishes for Gratiot Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 17 ft down. Phosphorus 9 µg/L. TSI 36.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 17ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 9µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 36 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Gratiot Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
70 ft
Surface area
1,453 acres
Stays via Stay22
Stays near Gratiot Lake
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Top-rated places to stay near Gratiot Lake
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Fish Species
Click a species to see every lake where it is documented.
Fishing Gratiot Lake
Water Quality Trend: Stable
Based on 7 years of monitoring (2016–2023).
Water clarity
Improving7 years
Phosphorus
Worsening+0.54 µg/L/yr7 years
Nearby Lakes in Keweenaw County
Frequently asked questions about Gratiot Lake
Where is Gratiot Lake?
- Gratiot Lake is a lake in Keweenaw County, Michigan. Its water-quality measurements are published by EGLE and shown on this page as reported.
What is the water quality of Gratiot Lake?
- Gratiot Lake in Keweenaw County, Michigan has water-quality measurements published by EGLE, shown here as reported. Water clarity: 17 ft visibility. Phosphorus: 9 µg/L. Maximum depth: 70 ft. Surface area: 1453.1 acres.
Is Gratiot Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is Gratiot Lake?
- Gratiot Lake has a maximum depth of 70 feet. The lake covers 1453.1 acres.
What fish are in Gratiot Lake?
- Fish species found in Gratiot Lake include Ninespine stickleback. Gratiot Lake is located in Keweenaw County, Michigan.
Explore Gratiot Lake across LakeQuality
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Where this data comes from
91 measurements from 1 monitoring station, 2016–2023. Retrieved from the EPA Water Quality Portal on 2026-08-26.
Collected and reported by
- Michigan EGLE - MiCorps
21MICH_MICORPS91 samples · 2016–2023
Analytical methods
- Phosphorus by Colorimetry
Monitoring station identifiers (1)
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.