Everything here comes from public state and federal records. This page explains exactly how the map is built, what it claims, what it does not claim, and how to check it. Figures computed 2026-09-03; page built 2026-09-03.
The Minnesota Pollution Control Agency has recorded PFAS above a health standard in groundwater monitoring wells at 95 named facilities — mostly county landfills, across the state.
The Minnesota Department of Health has never tested fish for PFAS in 935 lakes (789,089 acres) or 4,305 river miles in or downstream of those same sub-watersheds, across 60 counties.
208 of those lakes and 139 of those river reaches were sampled — fish were caught, tissue was analyzed, a result was published — for mercury or PCBs. Not for PFAS.
Both datasets are public. Neither agency publishes them joined.
| Dataset | Agency | Used for |
|---|---|---|
| Fish consumption guidance (LakeFinder FCA pages) | MDH via DNR | Per-lake advisories and which contaminants were named |
| Waterbody-specific guidelines: Rivers (PDF) | MDH | River advisories by reach |
| Lake survey reports (LakeFinder API) | DNR | Fish populations, catch per net, DNR normal ranges |
| DNR Hydrography | DNR / MN Geospatial Commons | Lake list, DOW numbers, acreage, coordinates, stream geometry |
| Groundwater Contamination Atlas | MPCA | Monitoring wells, exceedances, contamination area polygons |
| Closed landfills, remediation sites, institutional controls | MPCA | Contamination sources and cleanup status |
| Impaired waters, 303(d), 2024 | MPCA | Fish-tissue impairments for mercury, PCBs, PFOS |
| Watershed Boundary Dataset (HUC12) | USGS | Sub-watershed boundaries and downstream links |
| Toxics Release Inventory | EPA | Facilities reporting chemical releases |
| ECHO enforcement | EPA | Formal actions, penalties, compliance status |
Data as retrieved on the dates shown on each record. Agencies revise these datasets; the map is rebuilt weekly.
exceedance_count > 0) whose exceedance names a PFAS compound.
8,543 wells qualify statewide.tohuc field up to two steps downstream.A lake is treated as already tested for PFAS if MDH's guidance page names any PFAS compound at all, or if MPCA has listed it PFOS-impaired. In practice that usually means a single compound — PFOS — while the PFAS family contains thousands. A lake screened only for PFOS is counted here as tested and is excluded from the finding, even though the compounds MPCA is measuring in groundwater at these sites routinely include PFOA, PFHxS, PFHxA, PFBS and PFNA as well.
That choice makes the count smaller and the claim narrower. It is deliberate: every lake in this finding has had no PFAS compound looked for in its fish.
MPCA's field is exceedance_pct_max. Despite the name, its values are the
measured concentration divided by the health standard — a multiple,
not a percentage. This site displays them as multiples (×).
MPCA publishes no definition for the field, so it was verified arithmetically against
its own exceedance_value_list column, using trichloroethene wells at the
Lehillier / Mankato site, where the health-based value is 0.4 µg/L:
| Well | Measured | Measured ÷ 0.4 | MPCA field value |
|---|---|---|---|
| 4D | 7.6 µg/L | 19.0 | 19.0 |
| W30R | 1.2 µg/L | 3.0 | 3.0 |
| W28R | 0.66 µg/L | 1.65 | 1.65 |
| 5D | 0.6 µg/L | 1.5 | 1.5 |
A PFOS well at the same site confirms it independently: 0.007 µg/L against a field value of 3.04 implies a standard of 0.0023 µg/L, which is MDH's health-based value for PFOS.
So a well listed at 18,101× carries roughly eighteen thousand times the health standard for the compound in question. Large multiples are not errors: PFAS standards are set in parts per trillion, so even a very large multiple can be an ordinary concentration for landfill leachate. If MPCA's own definition of this field differs from the arithmetic above, write to the corrections address and it will be relabelled.
| Lake | County | Acres | Nearest PFAS exceedance | MPCA exceedance magnitude | Last sampled |
|---|---|---|---|---|---|
| Lake of the Woods (MN) | Lake of the Woods | 305,576 | Lake of the Woods County Landfill | 22,785% | 2020-04-22 |
| Mille Lacs | Mille Lacs | 128,250 | Hickory Grove Landfill | 18,101% | 2025-05-08 |
| Vermilion | St. Louis | 39,272 | Vermillion Modified Sanitary Landfill | 833% | 2025-10-08 |
| East Vermilion | St. Louis | 25,798 | Vermillion Modified Sanitary Landfill | 833% | 2025-10-08 |
| Cass | Beltrami | 15,958 | Leech Lake Landfill | 1,544% | 2026-06-01 |
| Otter Tail | Otter Tail | 14,079 | Northeast Otter Tail County Landfill | 20,253% | 2025-03-26 |
| West Vermilion | St. Louis | 11,368 | Vermillion Modified Sanitary Landfill | 833% | 2025-10-08 |
| Gull | Cass | 10,010 | Maple Landfill | 18,228% | 2025-11-06 |
| Whitefish | Crow Wing | 7,714 | Fifty Lakes Landfill | 1,013% | 2023-11-21 |
| West Battle | Otter Tail | 5,615 | Battle Lake Landfill | 663% | 2025-06-03 |
| Woman | Cass | 5,520 | Walker-Hackensack Landfill | 5,392% | 2025-05-22 |
| Rush | Otter Tail | 5,276 | Northeast Otter Tail County Landfill | 20,253% | 2025-03-26 |
Minnesota has 8,628 lakes over 25 acres in the DNR hydrography layer. 1,458 have a fish-tissue result of any kind. 7,170 have none. Separately, DNR has published 21,933 fish population surveys covering 3,321 lakes, and MPCA has 19,599 monitoring wells in its contamination atlas.
If something here is wrong, I want to fix it. Email mnwaterdata@gmail.com with the record and what is incorrect. Corrections are made within 48 hours and noted here. Agencies, facility operators, and anyone else named in this data are welcome to write.
This is an independent project. It is not affiliated with or endorsed by MDH, MPCA, DNR, EPA, USGS, or any company named in the underlying records.