Gratiot Lake
Keweenaw County, Michigan1,453 acresView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↓ down from A at the last regrade
- Oligotrophic
- #2 of 11 in the county
- 70 ft max depth
- Limited data
Gratiot Lake in Keweenaw County, Michigan has a water quality grade of B (Good). Water clarity: 17 ft visibility. Phosphorus: 9 µg/L. Maximum depth: 70 ft. Surface area: 1453.1 acres.
- Clarity
- 17 ft
- Max depth
- 70 ft
- Area
- 1,453 acres
- Type
- Oligotrophic
- Phosphorus
- 9 µg/L
- Trend
- → Stable
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Watch Gratiot Lake’s letter
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Gratiot Lake is a 1,453-acre cold, clear oligotrophic lake in Keweenaw County, Michigan with a maximum depth of 70 feet. Water quality is graded B based on 1 sampling years through 2023. 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. Grade methodology: LakeQuality methodology.
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 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.
The B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: B (Good)
Crystal clear, you can see 17 ft down. Phosphorus 9 µg/L. TSI 36. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 17 ft | Not graded |
| Phosphorus | 9 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 36 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 70 ft |
| Surface Area | 1,453 acres |
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Gratiot Lake
Water Quality Trend: → Stable
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.868 m/yr | 7 |
| Phosphorus | ↓ Declining | +0.54 µg/L/yr | 7 |
County Ranking
Ranked #2 of 11 lakes in Keweenaw County
Nearby Lakes in Keweenaw County
Frequently asked questions about Gratiot Lake
Where is Gratiot Lake?
- Gratiot Lake is a lake in Keweenaw County, Michigan. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Gratiot Lake?
- Gratiot Lake in Keweenaw County, Michigan has a water quality grade of B (Good). 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?
- The B is nutrients and algae, 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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Low nutrients, clear water. The letter is not a swimming clearance.
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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)
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.