Lake Lillinonah
Litchfield County, ConnecticutView mapDirections
CT DEEP publishes the water-quality measurements for Lake Lillinonah. Here is what has been measured.
- Impaired · Algal growth
- Public access
- Limited data
Lake Lillinonah in Litchfield County, Connecticut has water-quality measurements published by CT DEEP, shown here as reported. Water clarity: 8.3 ft visibility.
Lake Lillinonah is a lake in Litchfield County, Connecticut. Limited fish-species data available. Public access is available.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2024-08-27. Methodology: how these readings are compared.
Swimming conditions
No readingRecreation use not supported
Nutrient and algae readings are not a swimming clearance. Lake Lillinonah is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, nutrients (phosphorus, nitrogen), pCBs, taste, color, odor, trash. Check local advisories before you swim.
Whether Lake Lillinonah is safe to swim in today is a call for the Connecticut Department of Energy and Environmental Protection and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Lake Lillinonah
These are the measurements CT DEEP publishes for Lake Lillinonah, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 8.3 ft. TSI 47.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 8.3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 47 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
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Fishing Lake Lillinonah
EPA Impairment Status
Lake Lillinonah is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Fish consumption, Recreation.
Source: EPA ATTAINS assessment unit CT6000-00-5+L1_01 · Official waterbody report
Nearby Lakes in Litchfield County
Frequently asked questions about Lake Lillinonah
Where is Lake Lillinonah?
- Lake Lillinonah is a lake in Litchfield County, Connecticut. Its water-quality measurements are published by CT DEEP and shown on this page as reported.
What is the water quality of Lake Lillinonah?
- Lake Lillinonah in Litchfield County, Connecticut has water-quality measurements published by CT DEEP, shown here as reported. Water clarity: 8.3 ft visibility.
Is Lake Lillinonah safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Lake Lillinonah is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, nutrients (phosphorus, nitrogen), pCBs, taste, color, odor, trash. Check local advisories before you swim.
Can I fish at Lake Lillinonah?
- Public access to Lake Lillinonah is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Connecticut's fish and wildlife agency, so check its current regulations before you go.
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Where this data comes from
45 measurements from 3 monitoring stations, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- CT DEEP Volunteer Water Monitoring Program (Volunteer)
CTVOLMON44 samples · 2024 - North American Lake Management Society
NALMS1 sample · 2024
Monitoring station identifiers (3)
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
Impairment status from EPA ATTAINS 303(d) database