Shag Lake
Marquette County, MichiganView mapDirections
Not enough samples to grade — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. No letter yet. Here is what we do have.
- Impaired · Mercury
- 34 ft max depth
- Public access
- Limited data
Shag Lake in Marquette County, Michigan is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 14.3 ft visibility. Phosphorus: 10 µg/L.
- Clarity
- 14.3 ft
- Max depth
- ~34 ft est.
- Phosphorus
- 10 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Watch Shag Lake’s letter
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Why Shag Lake has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Shag Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity and phosphorus, but not algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by EGLE and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Shag Lake is a lake in Marquette County, Michigan with an estimated average depth of about 34 feet. Overall water quality is improving over recent sampling years. The lake supports 7 documented fish species including Blacknose shiner, Golden shiner, and Iowa darter. Public access is available.
Source: EPA Water Quality Portal sampling records, EGLE, last sampled 2023-09-23. Grade methodology: LakeQuality methodology.
What Shag Lake is good for
From access and monitoring records, not editorial picks.
- Clear water14.3 ft of visibility
- Fishing7 species recorded
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Shag Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
Water quality measurements for Shag Lake
These readings exist but are not enough for an A–F grade — see why.
Good clarity, visible to about 14.3 ft. Phosphorus 10 µg/L. TSI 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 14.3 ft | Not graded |
| Phosphorus | 10 µg/L | Not graded |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~34 ft est. |
| Average Depth | ~13 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Michigan has not published bathymetry for Shag Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Shag Lake
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +3.59 m/yr | 2 |
EPA Impairment Status
Shag Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MI040301100206-02 · Official waterbody report · Matched by proximity (0.76 km)
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Shag Lake under Clean Water Act (NPDES) discharge permits.
- Joe & SonsGwinn · 3 mi away · NPDES MIG080309
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Graded lakes near Shag Lake
Shag Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Marquette County
Frequently asked questions about Shag Lake
Where is Shag Lake?
- Shag Lake is a lake in Marquette County, Michigan. LakeQuality has not rated this lake (UNRATED) — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity.
What is the water quality grade for Shag Lake?
- Shag Lake in Marquette County, Michigan is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 14.3 ft visibility. Phosphorus: 10 µg/L.
Is Shag Lake safe to swim in?
- The letter is not a swimming clearance. Shag Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
How deep is Shag Lake?
- No published bathymetric survey covers Shag Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 34 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
What fish are in Shag Lake?
- Fish species found in Shag Lake include Blacknose shiner, Golden shiner, Iowa darter, Mimic shiner, Northern redbelly dace, White sucker, Yellow perch. Shag Lake is located in Marquette County, Michigan.
Explore Shag Lake across LakeQuality
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Where this data comes from
16 measurements from 1 monitoring station, 2022–2023. Retrieved from the EPA Water Quality Portal on 2026-08-26.
Collected and reported by
- Michigan EGLE - MiCorps
21MICH_MICORPS16 samples · 2022–2023
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.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)