Lake Quassapaug
New Haven County, Connecticut290 acresView mapDirections
CT DEEP publishes the water-quality measurements for Lake Quassapaug. Here is what has been measured.
- Mesotrophic
- Limited data
Lake Quassapaug in New Haven County, Connecticut has water-quality measurements published by CT DEEP, shown here as reported. Phosphorus: 15.5 µg/L. Chlorophyll-a (algae): 2.9 µg/L. Surface area: 290 acres.
Lake Quassapaug is a 290-acre mesotrophic lake in New Haven County, Connecticut. Compared to the 1 other monitored lakes in New Haven County, Lake Quassapaug ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2024-08-01. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLimited data
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 Lake Quassapaug 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 Quassapaug
These are the measurements CT DEEP publishes for Lake Quassapaug, 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 15.5 µg/L. Chlorophyll-a 2.9 µg/L. TSI 42.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 15.5µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.9µg/L | Measured, not scored 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. | 42 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
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Lake Details
Surface area
290 acres
No bathymetric survey has been published for Lake Quassapaug, so its depth is not documented here.
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Fishing Lake Quassapaug
Reservoir Info (USACE NID)
Lake Quassapaug is a man-made reservoir impounded by the Quassapaug Lake Dam (completed 1900), built primarily for recreation on the Eightmile Brook; earth-type dam, 24 ft tall and 125 ft long.
- Surface area
- 290 ac
- Normal storage
- 2,601 ac-ft
- Drainage area
- 1.82 sq mi
- Hazard class
- Significant
- Owner
- West Shore Owners Association
Source: USACE National Inventory of Dams, NID ID CT00329 · Operator website
Nearby Lakes in New Haven County
Frequently asked questions about Lake Quassapaug
Where is Lake Quassapaug?
- Lake Quassapaug is a lake in New Haven 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 Quassapaug?
- Lake Quassapaug in New Haven County, Connecticut has water-quality measurements published by CT DEEP, shown here as reported. Phosphorus: 15.5 µg/L. Chlorophyll-a (algae): 2.9 µg/L. Surface area: 290 acres.
Is Lake Quassapaug safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Lake Quassapaug across LakeQuality
More lakes in Connecticut
Other Lakes in Connecticut
Mesotrophic Lakes in Connecticut
Where this data comes from
40 measurements from 1 monitoring station, 2021–2024. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- Connecticut Department Of Energy And Environmental Protection
CT_DEP01_WQX40 samples · 2021–2024
Analytical methods
- Total Phosphorus After Block Digestion
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- Nitrate-Nitrite Nitrogen by Colorimetry
- Turbidity by Nephelometry
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.