Sudbury Reservoir
Worcester County, Massachusetts1,300 acresView mapDirections
MassDEP publishes the water-quality measurements for Sudbury Reservoir. Here is what has been measured.
- Oligotrophic
- Impaired · Mercury
- 49 ft max depth
- Public access
- Limited data
Sudbury Reservoir in Worcester County, Massachusetts has water-quality measurements published by MassDEP, shown here as reported. Chlorophyll-a (algae): 1.4 µg/L. Surface area: 1300 acres.
Sudbury Reservoir is a 1,300-acre cold, clear oligotrophic lake in Worcester County, Massachusetts with an estimated average depth of about 49 feet. 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. Methodology: how these readings are compared.
What Sudbury Reservoir is good for
From access and monitoring records, not editorial picks.
- Big water1,300 acres
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. 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.
Whether Sudbury Reservoir is safe to swim in today is a call for the Massachusetts Department of Environmental Protection and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Sudbury Reservoir
These are the measurements MassDEP publishes for Sudbury 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. Chlorophyll-a 1.4 µg/L. TSI 34.
| 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 | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | 1.4µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 34 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Sudbury Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~49 ft est.
Surface area
1,300 acres
Public access
Yes
Listed by MassDEP
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
Watershed (drainage) area
23 sq mi
HydroLAKES / HydroSHEDS
Shoreline
20 mi
HydroLAKES / HydroSHEDS
Elevation
259 ft
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.
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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
Designated uses not supporting: Aquatic life, Fish consumption.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MA82106 · Official waterbody report
Nearby Lakes in Worcester County
Frequently asked questions about Sudbury Reservoir
Where is Sudbury Reservoir?
- Sudbury Reservoir is a lake in Worcester County, Massachusetts. Its water-quality measurements are published by MassDEP and shown on this page as reported.
What is the water quality of Sudbury Reservoir?
- Sudbury Reservoir in Worcester County, Massachusetts has water-quality measurements published by MassDEP, shown here as reported. Chlorophyll-a (algae): 1.4 µg/L. Surface area: 1300 acres.
Is Sudbury Reservoir safe to swim in?
- Nutrient and algae readings are 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.
Can I fish at Sudbury Reservoir?
- Public access to Sudbury Reservoir is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Massachusetts's fish and wildlife agency, so check its current regulations before you go.
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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)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)