Onway Lake-Island Road
Rockingham County, New Hampshire194 acresView mapDirections
NHDES publishes the water-quality measurements for Onway Lake-Island Road. Here is what has been measured.
- Oligotrophic
- Impaired · Mercury
- Limited data
Onway Lake-Island Road in Rockingham County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 8.8 µg/L. Surface area: 194 acres.
Onway Lake-Island Road is a 194-acre cold, clear oligotrophic lake in Rockingham County, New Hampshire. Compared to the 50 other monitored lakes in Rockingham County, Onway Lake-Island Road ranks #12 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2025-07-01. 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. Onway Lake-Island Road is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, oxygen depletion (low DO), pH / acidity. Check local advisories before you swim.
Whether Onway Lake-Island Road is safe to swim in today is a call for the New Hampshire Department of Environmental Services and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Onway Lake-Island Road
These are the measurements NHDES publishes for Onway Lake-Island Road, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 8.8 µg/L. TSI 35.
| 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 | 8.8µg/L | Good GoodFairPoor |
| 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. | 35 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Onway Lake-Island Road
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
194 acres
No bathymetric survey has been published for Onway Lake-Island Road, so its depth is not documented here.
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Fishing Onway Lake-Island Road
Reservoir Info (USACE NID)
Onway Lake-Island Road is a man-made reservoir impounded by the Onway Lake Dam (completed 1915), built primarily for recreation on the Tr Lamprey River; concrete-type dam, 9 ft tall and 65 ft long.
- Surface area
- 194 ac
- Normal storage
- 2,100 ac-ft
- Max storage
- 2,600 ac-ft
- Drainage area
- 8.48 sq mi
- Hazard class
- Low
- Owner
- J AND D REALTY TRUST
Source: USACE National Inventory of Dams, NID ID NH00438 · Operator website · Matched by proximity (0.76 km)
EPA Impairment Status
Onway Lake-Island Road is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
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 NHLAK600030703-03-01 · Official waterbody report
Nearby Lakes in Rockingham County
Frequently asked questions about Onway Lake-Island Road
Where is Onway Lake-Island Road?
- Onway Lake-Island Road is a lake in Rockingham County, New Hampshire. Its water-quality measurements are published by NHDES and shown on this page as reported.
What is the water quality of Onway Lake-Island Road?
- Onway Lake-Island Road in Rockingham County, New Hampshire has water-quality measurements published by NHDES, shown here as reported. Phosphorus: 8.8 µg/L. Surface area: 194 acres.
Is Onway Lake-Island Road safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Onway Lake-Island Road is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, oxygen depletion (low DO), pH / acidity. Check local advisories before you swim.
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Where this data comes from
5 measurements from 1 monitoring station, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- New Hampshire Department Of Environmental Services (BEACH)
111133005 samples · 2021–2025
Analytical methods
- 10-115-01-1 F ~ LACHAT; Total Phosphorus- Manual persulfate digest
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