Rainbow Reservoir
Hartford County, Connecticut235 acresView mapDirections
CT DEEP publishes the water-quality measurements for Rainbow Reservoir. Here is what has been measured.
- Eutrophic
- Impaired · Hydrologic alteration
Rainbow Reservoir in Hartford County, Connecticut has water-quality measurements published by CT DEEP, shown here as reported. Phosphorus: 50 µg/L. Surface area: 234.5 acres.
Rainbow Reservoir is a 235-acre productive, nutrient-rich eutrophic lake in Hartford County, Connecticut. Compared to the 3 other monitored lakes in Hartford County, Rainbow Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-08-04. Methodology: how these readings are compared.
Swimming conditions
Readings onlyElevated nutrients
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. Rainbow Reservoir is listed impaired under Clean Water Act §303(d) (IR 4C) for hydrologic alteration. Check local advisories before you swim.
Whether Rainbow Reservoir 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 Rainbow Reservoir
These are the measurements CT DEEP publishes for Rainbow Reservoir, 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 50 µg/L. TSI 61.
| 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 | 50µg/L | Poor GoodFairPoor |
| 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. | 61 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Rainbow Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
235 acres
No bathymetric survey has been published for Rainbow Reservoir, so its depth is not documented here.
Stays via Stay22
Stays near Rainbow Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Rainbow Reservoir in Hartford 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Rainbow Reservoir are listed below.
Top-rated places to stay near Rainbow Reservoir
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Fishing Rainbow Reservoir
Reservoir Info (USACE NID)
Rainbow Reservoir is a man-made reservoir impounded by the Rainbow Reservoir Dam (completed 1925), built primarily for hydroelectric on the Farmington River; earth-type dam, 43 ft tall and 1,310 ft long.
- Surface area
- 234.5 ac
- Normal storage
- 4,800 ac-ft
- Max storage
- 9,400 ac-ft
- Drainage area
- 588 sq mi
- Hazard class
- High
- Owner
- The Farmington River Power Co.
Source: USACE National Inventory of Dams, NID ID CT00039 · Operator website
EPA Impairment Status
Rainbow Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 4C).
Causes of impairment
Designated uses not supporting: Aquatic life.
Source: EPA ATTAINS assessment unit CT4300-00-5+L5_01 · Official waterbody report
Nearby Lakes in Hartford County
Frequently asked questions about Rainbow Reservoir
Where is Rainbow Reservoir?
- Rainbow Reservoir is a lake in Hartford County, Connecticut. Its water-quality measurements are published by CT DEEP and shown on this page as reported.
What is the water quality of Rainbow Reservoir?
- Rainbow Reservoir in Hartford County, Connecticut has water-quality measurements published by CT DEEP, shown here as reported. Phosphorus: 50 µg/L. Surface area: 234.5 acres.
Is Rainbow Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Rainbow Reservoir is listed impaired under Clean Water Act §303(d) (IR 4C) for hydrologic alteration. Check local advisories before you swim.
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Where this data comes from
799 measurements from 11 monitoring stations, 2023–2025. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- Farmington River Watershed Association (Volunteer)
FRWA799 samples · 2023–2025
Analytical methods
- Total Phosphorus After Block Digestion
- Nitrate-Nitrite Nitrogen by Colorimetry
- Multiparameter Water Quality Sonde
- Metals in Water by ICP-AES
Monitoring station identifiers (11)
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