Middlesex Reservoir
Middlesex Reservoir in Union County, New Jersey has a water quality grade of D (Nutrient-rich). Water clarity: 3.6 ft visibility. Phosphorus: 173 µg/L. Chlorophyll-a (algae): 11.3 µg/L. Surface area: 87 acres.
- Clarity
- 3.6 ft
- Area
- 87 acres
- Type
- Eutrophic
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Middlesex Reservoir →
Middlesex Reservoir is a 87-acre productive, nutrient-rich eutrophic lake in Union County, New Jersey. Water quality is graded D based on 2 sampling years through 2023. Compared to the 1 other monitored lakes in Union County, Middlesex Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2023-11-06. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyBacteria advisory
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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Murky, only visible to about 3.6 ft. Phosphorus level: 173 µg/L. Chlorophyll-a: 11.3 µg/L. Trophic State Index: 64.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.6 ft | Not graded |
| Phosphorus | 173 µg/L | Poor |
| Chlorophyll-a (Algae) | 11.3 µg/L | Fair |
| Trophic State Index (TSI) | 64 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Middlesex Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Middlesex Reservoir in Union 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 Middlesex Reservoir are listed below.
Top-rated places to stay near Middlesex Reservoir
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 87 acres |
No bathymetric survey has been published for Middlesex Reservoir, so its depth is not documented here.
Fishing Middlesex Reservoir
Reservoir Info (USACE NID)
Middlesex Reservoir is a man-made reservoir impounded by the Robinson's Branch Reservoir Dam (completed 1907), built primarily for water supply on the Robinsons Branch; earth-type dam, 27 ft tall and 425 ft long.
- Surface area
- 87 ac
- Normal storage
- 608 ac-ft
- Max storage
- 1,269 ac-ft
- Drainage area
- 19.1 sq mi
- Hazard class
- High
- Owner
- County of Union
Source: USACE National Inventory of Dams, NID ID NJ00377 · Operator website · Matched by proximity (0.91 km)
EPA Impairment Status
Middlesex Reservoir 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 NJ02030104050080-01 · Official waterbody report · Matched by proximity (2.01 km)
County Ranking
Ranked #1 of 2 lakes in Union County
Nearby Lakes in Union County
Frequently asked questions about Middlesex Reservoir
Where is Middlesex Reservoir?
- Middlesex Reservoir is a lake in Union County, New Jersey. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Middlesex Reservoir?
- Middlesex Reservoir in Union County, New Jersey has a water quality grade of D (Nutrient-rich). Water clarity: 3.6 ft visibility. Phosphorus: 173 µg/L. Chlorophyll-a (algae): 11.3 µg/L. Surface area: 87 acres.
Is Middlesex Reservoir safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Middlesex Reservoir has a water quality grade of D (Nutrient-rich). Algae concentration (chlorophyll-a) is 11.3 µg/L. Always check local health department advisories before swimming.
Explore Middlesex Reservoir across LakeGrade
More New Jersey Lake Rankings
Other Grade D Lakes in New Jersey
Eutrophic Lakes in New Jersey
Where this data comes from
109 measurements from 4 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_BFBM109 samples · 2022–2023
Analytical methods
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
Monitoring station identifiers (4)
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