Fish Lake
Lincoln County, MontanaView mapDirections
Nutrients and algae sit mid-range for this region.
↓ down from A at the last regrade
- Mesotrophic
- #11 of 18 in the county
- 20 ft max depth
Fish Lake in Lincoln County, Montana has a water quality grade of C (Fair). Phosphorus: 8.1 µg/L. Chlorophyll-a (algae): 2.3 µg/L.
- Max depth
- ~20 ft est.
- Type
- Mesotrophic
- Phosphorus
- 8.1 µg/L
- Chlorophyll-a
- 2.3 µg/L
- Trend
- → Stable
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Watch Fish Lake’s letter
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Fish Lake is a mesotrophic lake in Lincoln County, Montana with an estimated average depth of about 20 feet. Water quality is graded C based on 3 sampling years through 2023. Phosphorus level is declining over recent sampling years. Compared to the 17 other monitored lakes in Lincoln County, Fish Lake ranks #11 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2023-07-24. Grade methodology: LakeQuality methodology.
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.
The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: C (Fair)
No clarity data. Phosphorus 8.1 µg/L. Chlorophyll-a 2.3 µg/L. TSI 37. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 8.1 µg/L | Good |
| Chlorophyll-a (Algae) | 2.3 µg/L | Fair |
| Trophic State Index (TSI) | 37 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~20 ft est. |
| Average Depth | ~15 ft est. |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Montana has not published bathymetry for Fish 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.
Fishing Fish Lake
Water Quality Trend: → Stable
Based on 11 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +1.42 µg/L/yr | 10 |
| Chlorophyll-a | ↑ Improving | -0.09 µg/L/yr | 11 |
County Ranking
Ranked #11 of 18 lakes in Lincoln County
Nearby Lakes in Lincoln County
Frequently asked questions about Fish Lake
Where is Fish Lake?
- Fish Lake is a lake in Lincoln County, Montana. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Fish Lake?
- Fish Lake in Lincoln County, Montana has a water quality grade of C (Fair). Phosphorus: 8.1 µg/L. Chlorophyll-a (algae): 2.3 µg/L.
Is Fish Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
How deep is Fish Lake?
- No published bathymetric survey covers Fish Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 20 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Fish Lake across LakeQuality
More Montana Lake Rankings
Other Grade C Lakes in Montana
Mesotrophic Lakes in Montana
Where this data comes from
22 measurements from 1 monitoring station, 2012–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana Watershed
MTWTRSHD_WQX22 samples · 2012–2023
Analytical methods
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 4500 N C ~ Persufate Method for Total Nitrogen
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
Lake size & watershed from HydroLAKES (HydroSHEDS)