Long Lake
Washington County, MaineView mapDirections
Maine DEP publishes the water-quality measurements for Long Lake. Here is what has been measured.
- Mesotrophic
- Public access
Long Lake in Washington County, Maine has water-quality measurements published by Maine DEP, shown here as reported. Water clarity: 15.6 ft visibility. Phosphorus: 8.5 µg/L. Chlorophyll-a (algae): 3 µg/L.
Long Lake is a mesotrophic lake in Washington County, Maine. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 10 other monitored lakes in Washington County, Long Lake ranks #8 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-09-24. Methodology: how these readings are compared.
What Long Lake is good for
From access and monitoring records, not editorial picks.
- Clear water15.6 ft of visibility
Swimming conditions
Readings onlyLow 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 Long Lake is safe to swim in today is a call for the Maine Department of Environmental Protection and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Long Lake
These are the measurements Maine DEP publishes for Long 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 15.6 ft down. Phosphorus 8.5 µg/L. Chlorophyll-a 3 µg/L. TSI 38.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 15.6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 8.5µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 3µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 38 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Long Lake
Answers come straight from the public measurements and survey records on this page.
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Stays near Long Lake
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Fishing Long Lake
Water Quality Trend: Improving
Based on 6 years of monitoring (2020–2025).
Water clarity
Stable6 years
Phosphorus
Improving-0.29 µg/L/yr6 years
Chlorophyll-a
Improving-0.07 µg/L/yr6 years
Nearby Lakes in Washington County
Frequently asked questions about Long Lake
Where is Long Lake?
- Long Lake is a lake in Washington County, Maine. Its water-quality measurements are published by Maine DEP and shown on this page as reported.
What is the water quality of Long Lake?
- Long Lake in Washington County, Maine has water-quality measurements published by Maine DEP, shown here as reported. Water clarity: 15.6 ft visibility. Phosphorus: 8.5 µg/L. Chlorophyll-a (algae): 3 µg/L.
Is Long Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Can I fish at Long Lake?
- Public access to Long Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Maine's fish and wildlife agency, so check its current regulations before you go.
Explore Long Lake across LakeQuality
More lakes in Maine
Other Lakes in Maine
Mesotrophic Lakes in Maine
Where this data comes from
98 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Submitting organization not recorded for these samples98 samples · 2020–2025
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.