Rainbow Reservoir
Rainbow Reservoir in Hartford County, Connecticut has a water quality grade of D (Nutrient-rich). Phosphorus: 50 µg/L. Surface area: 234.5 acres.
- Area
- 235 acres
- Type
- Eutrophic
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Rainbow Reservoir →
Rainbow Reservoir is a 235-acre productive, nutrient-rich eutrophic lake in Hartford County, Connecticut. Water quality is graded D based on 2 sampling years through 2025. 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. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyElevated nutrients
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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
No clarity data. Phosphorus level: 50 µg/L. Trophic State Index: 61.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 50 µg/L | Poor |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 61 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay 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 grade measures nutrients and algae, not lodging — cabins and rentals around Rainbow Reservoir are listed below.
Top-rated places to stay near Rainbow Reservoir
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 235 acres |
No bathymetric survey has been published for Rainbow Reservoir, so its depth is not documented here.
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
Source: EPA ATTAINS assessment unit CT4300-00-5+L5_01 · Official waterbody report · Matched by proximity (1.3 km)
County Ranking
Ranked #1 of 4 lakes in Hartford County
Nearby Lakes in Hartford County
Frequently asked questions about Rainbow Reservoir
Where is Rainbow Reservoir?
- Rainbow Reservoir is a lake in Hartford County, Connecticut. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Rainbow Reservoir?
- Rainbow Reservoir in Hartford County, Connecticut has a water quality grade of D (Nutrient-rich). Phosphorus: 50 µg/L. Surface area: 234.5 acres.
Is Rainbow Reservoir safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Rainbow Reservoir has a water quality grade of D (Nutrient-rich). Always check local health department advisories before swimming.
Explore Rainbow Reservoir across LakeGrade
More Connecticut Lake Rankings
Other Grade D Lakes in Connecticut
Eutrophic Lakes in Connecticut
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)
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
Impairment status from EPA ATTAINS 303(d) database