Fish Lake
Lincoln County, MontanaView mapDirections
Montana DEQ publishes the water-quality measurements for Fish Lake. Here is what has been measured.
- Mesotrophic
- 20 ft max depth
Ask about Fish Lake
Answers come straight from the public measurements and survey records on this page.
Fish Lake in Lincoln County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 8.1 µg/L. Chlorophyll-a (algae): 2.3 µg/L.
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Fish Lake is a mesotrophic lake in Lincoln County, Montana with an estimated average depth of about 20 feet. 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 conditions
Readings onlyModerate algae
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 Fish Lake is safe to swim in today is a call for the Montana Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Fish Lake
These are the measurements Montana DEQ publishes for Fish Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 8.1 µg/L. Chlorophyll-a 2.3 µg/L. TSI 37.
| Metric | Value | EPA condition class |
|---|---|---|
| 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 |
Nearby Lakes in Lincoln County
Frequently asked questions about Fish Lake
Where is Fish Lake?
- Fish Lake is a lake in Lincoln County, Montana. Its water-quality measurements are published by Montana DEQ and shown on this page as reported.
What is the water quality of Fish Lake?
- Fish Lake in Lincoln County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 8.1 µg/L. Chlorophyll-a (algae): 2.3 µg/L.
Is Fish Lake safe to swim in?
- Nutrient and algae readings are 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
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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)
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.
Other records on this page
Lake size & watershed from HydroLAKES (HydroSHEDS)