Wachusett Reservoir
Worcester County, Massachusetts4,160 acresView mapDirections
MassDEP publishes the water-quality measurements for Wachusett Reservoir. Here is what has been measured.
- Impaired · Algal growth
- Limited data
Wachusett Reservoir in Worcester County, Massachusetts has water-quality measurements published by MassDEP, shown here as reported. Water clarity: 25.8 ft visibility. Surface area: 4160 acres.
Wachusett Reservoir is a 4,160-acre lake in Worcester County, Massachusetts. Overall water quality is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, MassDEP, last sampled 2023-07-31. Methodology: how these readings are compared.
What Wachusett Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water25.8 ft of visibility
- Big water4,160 acres
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Wachusett Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for algal growth, mercury, nuisance exotic species. Check local advisories before you swim.
Whether Wachusett 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 Wachusett Reservoir
These are the measurements MassDEP publishes for Wachusett Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 25.8 ft down. TSI 30.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 25.8ft | Measured, not scored 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) | 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. | 30 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Wachusett Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
4,160 acres
No bathymetric survey has been published for Wachusett Reservoir, so its depth is not documented here.
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Fishing Wachusett Reservoir
Water quality readings over time
2 seasons of samples on record (2022–2023). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening2 years
Reservoir Info (USACE NID)
Wachusett Reservoir is a man-made reservoir impounded by the Wachusett Reservoir Dam (completed 1906), built primarily for water supply on the Nashua River; stone-type dam, 114 ft tall and 944 ft long.
- Surface area
- 4,160 ac
- Normal storage
- 187,000 ac-ft
- Max storage
- 250,000 ac-ft
- Drainage area
- 121 sq mi
- Hazard class
- High
- Owner
- MA Department of Conservation and Recreation
Source: USACE National Inventory of Dams, NID ID MA00886 · Operator website
EPA Impairment Status
Wachusett 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 MA81147 · Official waterbody report
Nearby Lakes in Worcester County
Frequently asked questions about Wachusett Reservoir
Where is Wachusett Reservoir?
- Wachusett 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 Wachusett Reservoir?
- Wachusett Reservoir in Worcester County, Massachusetts has water-quality measurements published by MassDEP, shown here as reported. Water clarity: 25.8 ft visibility. Surface area: 4160 acres.
Is Wachusett Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Wachusett Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for algal growth, mercury, nuisance exotic species. Check local advisories before you swim.
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Where this data comes from
20 measurements from 1 monitoring station, 2022–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North American Lake Management Society
NALMS20 samples · 2022–2023
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