Quonnipaug Lake
Quonnipaug Lake in New Haven County, Connecticut has a water quality grade of C (Fair). Phosphorus: 22 µg/L. Chlorophyll-a (algae): 2.7 µg/L. Surface area: 111.6 acres.
- Area
- 112 acres
- Type
- Mesotrophic
- Public access
- Yes
Quonnipaug Lake is a 112-acre mesotrophic lake in New Haven County, Connecticut. Water quality is graded C based on 2 sampling years through 2023. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 1 other monitored lakes in New Haven County, Quonnipaug Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2023-07-11. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
No clarity data. Phosphorus level: 22 µg/L. Chlorophyll-a: 2.7 µg/L. Trophic State Index: 45.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 22 µg/L | Fair |
| Chlorophyll-a (Algae) | 2.7 µg/L | Not graded |
| Trophic State Index (TSI) | 45 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Quonnipaug Lake
Compare lakeside cabins, hotels, and vacation rentals near Quonnipaug Lake in New Haven County, Connecticut — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 112 acres |
| Public Access | Yes |
No bathymetric survey has been published for Quonnipaug Lake, so its depth is not documented here.
Recreation & Access
- Quonnipaug LakePublic
Named access points from the USGS National Boat Ramps inventory, snapped within 5 km. More lakes with boat ramps
Fishing Quonnipaug Lake
Reservoir Info (USACE NID)
Quonnipaug Lake is a man-made reservoir impounded by the Quonnipaug Lake Dam (completed 1850), built primarily for recreation on the West River; masonry-type dam, 5 ft tall and 110 ft long.
- Surface area
- 111.6 ac
- Normal storage
- 336 ac-ft
- Max storage
- 336 ac-ft
- Drainage area
- 2.63 sq mi
- Hazard class
- Significant
- Owner
- Town of Guilford
Source: USACE National Inventory of Dams, NID ID CT00411 · Operator website
County Ranking
Ranked #2 of 2 lakes in New Haven County
Nearby Lakes in New Haven County
Frequently asked questions about Quonnipaug Lake
Where is Quonnipaug Lake?
- Quonnipaug Lake is a lake in New Haven County, Connecticut. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Quonnipaug Lake?
- Quonnipaug Lake in New Haven County, Connecticut has a water quality grade of C (Fair). Phosphorus: 22 µg/L. Chlorophyll-a (algae): 2.7 µg/L. Surface area: 111.6 acres.
Is Quonnipaug Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Quonnipaug Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 2.7 µg/L. Always check local health department advisories before swimming.
Are there boat ramps on Quonnipaug Lake?
- Quonnipaug Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Quonnipaug Lake. Public access is listed as yes.
Explore Quonnipaug Lake across LakeGrade
More Connecticut Lake Rankings
Other Grade C Lakes in Connecticut
Mesotrophic Lakes in Connecticut
Where this data comes from
10 measurements from 1 monitoring station, 2023. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- Connecticut Department Of Energy And Environmental Protection
CT_DEP01_WQX10 samples · 2023
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)
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
Named boat-access points from the USGS National Boat Ramps inventory