Lake Iroquois
Chittenden County, Vermont229 acresView mapDirections
Nutrients and algae sit mid-range for this region.
↓ down from B at the last regrade
- Eutrophic
- Impaired · Algal growth
- #4 of 8 in the county
- 54 ft max depth
- Public access
Lake Iroquois in Chittenden County, Vermont has a water quality grade of C (Fair). Water clarity: 11.8 ft visibility. Phosphorus: 19.1 µg/L. Chlorophyll-a (algae): 8.4 µg/L. Surface area: 229 acres.
- Clarity
- 11.8 ft
- Max depth
- ~54 ft est.
- Area
- 229 acres
- Type
- Eutrophic
- Phosphorus
- 19.1 µg/L
- Chlorophyll-a
- 8.4 µg/L
- Trend
- → Stable
- Public access
- Yes
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Watch Lake Iroquois’s letter
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Lake Iroquois is a 229-acre productive, nutrient-rich eutrophic lake in Chittenden County, Vermont with an estimated average depth of about 54 feet. Water quality is graded C based on 2 sampling years through 2025. Phosphorus level is declining over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 7 other monitored lakes in Chittenden County, Lake Iroquois ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, VT DEC, last sampled 2025-08-18. Grade methodology: LakeQuality methodology.
What Lake Iroquois is good for
From access and monitoring records, not editorial picks.
- Clear water11.8 ft of visibility
- Boat launch1 documented ramp
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. Lake Iroquois is listed impaired under Clean Water Act §303(d) (IR 4C) for algal growth, nuisance exotic species. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Good clarity, visible to about 11.8 ft. Phosphorus 19.1 µg/L. Chlorophyll-a 8.4 µg/L. TSI 47. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.8 ft | Not graded |
| Phosphorus | 19.1 µg/L | Fair |
| Chlorophyll-a (Algae) | 8.4 µg/L | Fair |
| Trophic State Index (TSI) | 47 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~54 ft est. |
| Average Depth | ~19 ft est. |
| Surface Area | 229 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Vermont has not published bathymetry for Lake Iroquois.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Lake IroquoisPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Lake Iroquois
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.064 m/yr | 6 |
| Phosphorus | ↓ Declining | +1.36 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -0.76 µg/L/yr | 6 |
Reservoir Info (USACE NID)
Lake Iroquois is a man-made reservoir impounded by the Lake Iroquois (completed 1870), built primarily for other on the Patrick Brook; concrete-type dam, 7 ft tall and 98 ft long.
- Surface area
- 229 ac
- Normal storage
- 0 ac-ft
- Max storage
- 1,515 ac-ft
- Drainage area
- 3.78 sq mi
- Hazard class
- Low
- Owner
- IROQUOIS MANUFACTURING CO
All listed purposes: Other;Recreation.
Source: USACE National Inventory of Dams, NID ID VT00060 · Operator website
EPA Impairment Status
Lake Iroquois is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 4C).
Causes of impairment
Source: EPA ATTAINS assessment unit VT05-11L02_02 · Official waterbody report
County Ranking
Ranked #4 of 8 lakes in Chittenden County
Nearby Lakes in Chittenden County
Frequently asked questions about Lake Iroquois
Where is Lake Iroquois?
- Lake Iroquois is a lake in Chittenden County, Vermont. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake Iroquois?
- Lake Iroquois in Chittenden County, Vermont has a water quality grade of C (Fair). Water clarity: 11.8 ft visibility. Phosphorus: 19.1 µg/L. Chlorophyll-a (algae): 8.4 µg/L. Surface area: 229 acres.
Is Lake Iroquois safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Lake Iroquois is listed impaired under Clean Water Act §303(d) (IR 4C) for algal growth, nuisance exotic species. Check local advisories before you swim.
How deep is Lake Iroquois?
- No published bathymetric survey covers Lake Iroquois, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 54 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 229 acres.
Are there boat ramps on Lake Iroquois?
- Lake Iroquois has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Lake Iroquois. Public access is listed as yes.
Explore Lake Iroquois across LakeQuality
More Vermont Lake Rankings
Other Grade C Lakes in Vermont
Eutrophic Lakes in Vermont
Where this data comes from
243 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Vermont Dept of Environmental Conservation
1VTDECWQ243 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
- 2130 B ~ Nephelometric Method
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory