Etra Lake
Etra Lake in Mercer County, New Jersey has a water quality grade of F (Algae-prone). Water clarity: 3.9 ft visibility. Phosphorus: 46.6 µg/L. Chlorophyll-a (algae): 35.4 µg/L. Surface area: 21 acres.
- Clarity
- 3.9 ft
- Area
- 21 acres
- Type
- Hypereutrophic
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Etra Lake →
Etra Lake is a 21-acre highly nutrient-loaded hypereutrophic lake in Mercer County, New Jersey. Water quality is graded F based on 2 sampling years through 2023. Compared to the 14 other monitored lakes in Mercer County, Etra Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2023-10-11. Grade methodology: LakeGrade methodology.
Watch Etra Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
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.
Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom
Water Quality Grade: F (Algae-prone)
Murky, only visible to about 3.9 ft. Phosphorus level: 46.6 µg/L. Chlorophyll-a: 35.4 µg/L. Trophic State Index: 61.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.9 ft | Not graded |
| Phosphorus | 46.6 µg/L | Fair |
| Chlorophyll-a (Algae) | 35.4 µg/L | Poor |
| Trophic State Index (TSI) | 61 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Etra Lake
Compare lakeside cabins, hotels, and vacation rentals near Etra Lake in Mercer County, New Jersey — 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 Etra Lake are listed below.
Top-rated places to stay near Etra Lake
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 | 21 acres |
No bathymetric survey has been published for Etra Lake, so its depth is not documented here.
Fishing Etra Lake
Reservoir Info (USACE NID)
Etra Lake is a man-made reservoir impounded by the Etra Mill Dam (completed 1930), built primarily for recreation on the Rocky Brook; earth-type dam, 11 ft tall and 300 ft long.
- Surface area
- 21 ac
- Normal storage
- 66 ac-ft
- Drainage area
- 9.1 sq mi
- Hazard class
- Low
- Owner
- Township of East Windsor
Source: USACE National Inventory of Dams, NID ID NJ00298 · Operator website · Matched by proximity (0.18 km)
EPA Impairment Status
Etra Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit NJ02030105100050-01 · Official waterbody report · Matched by proximity (0.79 km)
County Ranking
Ranked #5 of 15 lakes in Mercer County
Nearby Lakes in Mercer County
Frequently asked questions about Etra Lake
Where is Etra Lake?
- Etra Lake is a lake in Mercer County, New Jersey. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Etra Lake?
- Etra Lake in Mercer County, New Jersey has a water quality grade of F (Algae-prone). Water clarity: 3.9 ft visibility. Phosphorus: 46.6 µg/L. Chlorophyll-a (algae): 35.4 µg/L. Surface area: 21 acres.
Is Etra Lake safe to swim in?
- Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom. Etra Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 35.4 µg/L. Always check local health department advisories before swimming.
Explore Etra Lake across LakeGrade
More New Jersey Lake Rankings
Other Grade F Lakes in New Jersey
Hypereutrophic Lakes in New Jersey
Where this data comes from
56 measurements from 2 monitoring stations, 2022–2023. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- NJDEP Bureau of Freshwater and Biological Monitoring
NJDEP_BFBM56 samples · 2022–2023
Analytical methods
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
Monitoring station identifiers (2)
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