Isle la Motte Lake
Grand Isle County, VermontView mapDirections
Nutrients and algae sit mid-range for this region.
↓ down from A at the last regrade
- Mesotrophic
- Impaired · Mercury
- #3 of 3 in the county
- Public access
Isle la Motte Lake in Grand Isle County, Vermont has a water quality grade of C (Fair). Water clarity: 15.1 ft visibility. Phosphorus: 19.9 µg/L. Chlorophyll-a (algae): 3.2 µg/L.
- Clarity
- 15.1 ft
- Type
- Mesotrophic
- Phosphorus
- 19.9 µg/L
- Chlorophyll-a
- 3.2 µg/L
- Trend
- ↓ Declining
- Public access
- Yes
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Isle la Motte Lake is a mesotrophic lake in Grand Isle County, Vermont. Water quality is graded C based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 2 other monitored lakes in Grand Isle County, Isle la Motte Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, VT DEC, last sampled 2025-08-21. Grade methodology: LakeQuality methodology.
What Isle la Motte Lake is good for
From access and monitoring records, not editorial picks.
- Clear water15.1 ft of visibility
- Boat launch2 documented ramps
Swimming Safety
Grade onlyModerate
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.
The C is nutrients and algae, not a swimming clearance. Isle la Motte Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nuisance exotic species, nutrients (phosphorus, nitrogen), pCBs. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Crystal clear, you can see 15.1 ft down. Phosphorus 19.9 µg/L. Chlorophyll-a 3.2 µg/L. TSI 42. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 15.1 ft | Not graded |
| Phosphorus | 19.9 µg/L | Fair |
| Chlorophyll-a (Algae) | 3.2 µg/L | Good |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Recreation & Access
- Holcomb BayPublic
- Stoney PointPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Isle la Motte Lake
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.34 m/yr | 5 |
| Phosphorus | ↑ Improving | -0.99 µg/L/yr | 5 |
| Chlorophyll-a | ↓ Declining | +0.4 µg/L/yr | 5 |
EPA Impairment Status
Isle la Motte 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 VT05-04L02_02 · Official waterbody report · Matched by proximity (1.83 km)
County Ranking
Ranked #3 of 3 lakes in Grand Isle County
Nearby Lakes in Grand Isle County
Frequently asked questions about Isle la Motte Lake
Where is Isle la Motte Lake?
- Isle la Motte Lake is a lake in Grand Isle County, Vermont. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Isle la Motte Lake?
- Isle la Motte Lake in Grand Isle County, Vermont has a water quality grade of C (Fair). Water clarity: 15.1 ft visibility. Phosphorus: 19.9 µg/L. Chlorophyll-a (algae): 3.2 µg/L.
Is Isle la Motte Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Isle la Motte Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nuisance exotic species, nutrients (phosphorus, nitrogen), pCBs. Check local advisories before you swim.
Are there boat ramps on Isle la Motte Lake?
- Isle la Motte Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Holcomb Bay, Stoney Point. Public access is listed as yes.
Explore Isle la Motte Lake across LakeQuality
More Vermont Lake Rankings
Other Grade C Lakes in Vermont
Mesotrophic Lakes in Vermont
Where this data comes from
121 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Vermont Dept of Environmental Conservation
1VTDECWQ121 samples · 2020–2025
Analytical methods
- EPA approved Alternate Test Procedure for 4500 P H. Has a 28 day hold without acid preservation.
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
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