South Reservoir
Middlesex County, Massachusetts80 acresView mapDirections
MassDEP publishes the water-quality measurements for South Reservoir. Here is what has been measured.
- Mesotrophic
- 42 ft max depth
- Limited data
South Reservoir in Middlesex County, Massachusetts has water-quality measurements published by MassDEP, shown here as reported. Chlorophyll-a (algae): 2.5 µg/L. Surface area: 80 acres.
South Reservoir is a 80-acre mesotrophic lake in Middlesex County, Massachusetts with an estimated average depth of about 42 feet. Compared to the 10 other monitored lakes in Middlesex County, South Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, MassDEP, last sampled 2017-09-14. Methodology: how these readings are compared.
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. Check local advisories before you swim.
Whether South 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 South Reservoir
These are the measurements MassDEP publishes for South 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 2.5 µg/L. TSI 40.
| 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) | 2.5µg/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. | 40 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about South Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~42 ft est.
Surface area
80 acres
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Massachusetts has not published bathymetry for South Reservoir.
Lake Size & Watershed
Watershed (drainage) area
0 sq mi
HydroLAKES / HydroSHEDS
Shoreline
3.5 mi
HydroLAKES / HydroSHEDS
Elevation
171 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 South Reservoir
Reservoir Info (USACE NID)
South Reservoir is a man-made reservoir impounded by the South Reservoir Dam (completed 1882), built primarily for water supply on the Meetinghouse Brook; earth-type dam, 45 ft tall and 1,000 ft long.
- Surface area
- 80 ac
- Normal storage
- 1,614 ac-ft
- Max storage
- 2,040 ac-ft
- Drainage area
- 0.77 sq mi
- Hazard class
- High
- Owner
- Town of Winchester
Source: USACE National Inventory of Dams, NID ID MA00453 · Operator website
Nearby Lakes in Middlesex County
Frequently asked questions about South Reservoir
Where is South Reservoir?
- South Reservoir is a lake in Middlesex County, Massachusetts. Its water-quality measurements are published by MassDEP and shown on this page as reported.
What is the water quality of South Reservoir?
- South Reservoir in Middlesex County, Massachusetts has water-quality measurements published by MassDEP, shown here as reported. Chlorophyll-a (algae): 2.5 µg/L. Surface area: 80 acres.
Is South Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is South Reservoir?
- No published bathymetric survey covers South Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 42 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 80 acres.
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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
Lake size & watershed from HydroLAKES (HydroSHEDS)