Sudbury Reservoir
Worcester County, Massachusetts1,300 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Oligotrophic
- Impaired · Mercury
- #14 of 24 in the county
- 49 ft max depth
- Public access
- Limited data
Sudbury Reservoir in Worcester County, Massachusetts has a water quality grade of A (Excellent). Chlorophyll-a (algae): 1.4 µg/L. Surface area: 1300 acres.
- Max depth
- ~49 ft est.
- Area
- 1,300 acres
- Type
- Oligotrophic
- Chlorophyll-a
- 1.4 µg/L
- Public access
- Yes
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Watch Sudbury Reservoir’s letter
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Sudbury Reservoir is a 1,300-acre cold, clear oligotrophic lake in Worcester County, Massachusetts with an estimated average depth of about 49 feet. Water quality is graded A based on 1 sampling years through 2017. Limited fish-species data available. Public access is available. Compared to the 23 other monitored lakes in Worcester County, Sudbury Reservoir ranks #14 for water quality.
Source: EPA Water Quality Portal sampling records, MassDEP, last sampled 2017-09-26. Grade methodology: LakeQuality methodology.
What Sudbury Reservoir is good for
From access and monitoring records, not editorial picks.
- Big water1,300 acres
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.
The A is nutrients and algae, not a swimming clearance. Sudbury Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury, noxious aquatic plants, nuisance exotic species. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
No clarity data. Chlorophyll-a 1.4 µg/L. TSI 34. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | 1.4 µg/L | Good |
| Trophic State Index (TSI) | 34 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~49 ft est. |
| Average Depth | ~30 ft est. |
| Surface Area | 1,300 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Massachusetts has not published bathymetry for Sudbury Reservoir.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Sudbury Reservoir
Reservoir Info (USACE NID)
Sudbury Reservoir is a man-made reservoir impounded by the Sudbury Reservoir Dam (completed 1899), built primarily for water supply on the Stony Brook; earth-type dam, 77 ft tall and 2,000 ft long.
- Surface area
- 1,300 ac
- Normal storage
- 22,260 ac-ft
- Max storage
- 33,020 ac-ft
- Drainage area
- 22.7 sq mi
- Hazard class
- High
- Owner
- MA Department of Conservation and Recreation
Source: USACE National Inventory of Dams, NID ID MA00741 · Operator website
EPA Impairment Status
Sudbury Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MA82106 · Official waterbody report
County Ranking
Ranked #14 of 24 lakes in Worcester County
Nearby Lakes in Worcester County
Frequently asked questions about Sudbury Reservoir
Where is Sudbury Reservoir?
- Sudbury Reservoir is a lake in Worcester County, Massachusetts. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Sudbury Reservoir?
- Sudbury Reservoir in Worcester County, Massachusetts has a water quality grade of A (Excellent). Chlorophyll-a (algae): 1.4 µg/L. Surface area: 1300 acres.
Is Sudbury Reservoir safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Sudbury Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury, noxious aquatic plants, nuisance exotic species. Check local advisories before you swim.
How deep is Sudbury Reservoir?
- No published bathymetric survey covers Sudbury Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 49 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 1300 acres.
Explore Sudbury Reservoir across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Massachusetts's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
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Where this data comes from
3 measurements from 1 monitoring station, 2017. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Massachusetts Department of Environmental Protection (MassDEP)
MASSDEP3 samples · 2017
Analytical methods
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)