Knowles Pond-Deep Spot
Knowles Pond-Deep Spot in Merrimack County, New Hampshire has a water quality grade of B (Good). Phosphorus: 8 µg/L. Chlorophyll-a (algae): 2.8 µg/L. Surface area: 56 acres.
- Area
- 56 acres
- Type
- Oligotrophic
- Public access
- Yes
Knowles Pond-Deep Spot is a 56-acre cold, clear oligotrophic lake in Merrimack County, New Hampshire. Water quality is graded B based on 1 sampling years through 2024. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 40 other monitored lakes in Merrimack County, Knowles Pond-Deep Spot ranks #10 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2024-07-22. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
No clarity data. Phosphorus level: 8 µg/L. Chlorophyll-a: 2.8 µg/L. Trophic State Index: 37.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 8 µg/L | Good |
| Chlorophyll-a (Algae) | 2.8 µg/L | Not graded |
| Trophic State Index (TSI) | 37 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Knowles Pond-Deep Spot
Compare lakeside cabins, hotels, and vacation rentals near Knowles Pond-Deep Spot in Merrimack County, New Hampshire — 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.
Top-rated places to stay near Knowles Pond-Deep Spot
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 56 acres |
| Public Access | Yes |
No bathymetric survey has been published for Knowles Pond-Deep Spot, so its depth is not documented here.
Recreation & Access
- TiltonPublic
Named access points from the USGS National Boat Ramps inventory, snapped within 5 km. More lakes with boat ramps
Fishing Knowles Pond-Deep Spot
Reservoir Info (USACE NID)
Knowles Pond-Deep Spot is a man-made reservoir impounded by the Knowles Pond Dam (completed 1935), built primarily for recreation on the Tr Williams Brook; earth-type dam, 11 ft tall and 350 ft long.
- Surface area
- 56 ac
- Normal storage
- 182 ac-ft
- Max storage
- 237 ac-ft
- Drainage area
- 0.32 sq mi
- Hazard class
- Low
- Owner
- TOWN OF NORTHFIELD
Source: USACE National Inventory of Dams, NID ID NH00367 · Operator website · Matched by proximity (0.47 km)
EPA Impairment Status
Knowles Pond-Deep Spot is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit NHIMP700020203-01 · Official waterbody report · Matched by proximity (0.02 km)
County Ranking
Ranked #10 of 41 lakes in Merrimack County
Nearby Lakes in Merrimack County
Frequently asked questions about Knowles Pond-Deep Spot
Where is Knowles Pond-Deep Spot?
- Knowles Pond-Deep Spot is a lake in Merrimack County, New Hampshire. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Knowles Pond-Deep Spot?
- Knowles Pond-Deep Spot in Merrimack County, New Hampshire has a water quality grade of B (Good). Phosphorus: 8 µg/L. Chlorophyll-a (algae): 2.8 µg/L. Surface area: 56 acres.
Is Knowles Pond-Deep Spot safe to swim in?
- Good for swimming, clear water with low algae levels. Knowles Pond-Deep Spot has a water quality grade of B (Good). Algae concentration (chlorophyll-a) is 2.8 µg/L. Always check local health department advisories before swimming.
Are there boat ramps on Knowles Pond-Deep Spot?
- Knowles Pond-Deep Spot has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Tilton. Public access is listed as yes.
Explore Knowles Pond-Deep Spot across LakeGrade
More New Hampshire Lake Rankings
Top 25 by overall water quality score
Top 25 by Secchi water clarity
Grade A/B + low algae filter
Panfish-rich, public access
Full state directory
Other Grade B Lakes in New Hampshire
Oligotrophic Lakes in New Hampshire
Where this data comes from
29 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- New Hampshire Department Of Environmental Services (BEACH)
1111330029 samples · 2020–2024
Analytical methods
- 10-115-01-1 F ~ LACHAT; Total Phosphorus- Manual persulfate digest
- CHLOROPHYLL A-B-C DETERMINATION (MODIFIED)
Monitoring station identifiers (1)
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
Named boat-access points from the USGS National Boat Ramps inventory