Lake Climate & Long-Term Trends
Which Minnesota and Wisconsin lakes are getting cleaner — and which are getting worse. Trends calculated from EPA Water Quality Portal samples, year by year. Every lake page links to a full chart with sources.
Most improving
Largest relative improvement per year on any single metric.
- FMeeker County, Minnesota · Water Clarity↑ Improving+2.03 m/yr
- DMeeker County, Minnesota · Water Clarity↑ Improving+2.10 m/yr
- ACarlton County, Minnesota · Water Clarity↑ Improving+1.94 m/yr
- CCarlton County, Minnesota · Water Clarity↑ Improving+1.96 m/yr
- BStearns County, Minnesota · Water Clarity↑ Improving+1.14 m/yr
- CCarlton County, Minnesota · Water Clarity↑ Improving+2.24 m/yr
- DHennepin County, Minnesota · Phosphorus↑ Improving-63.67 µg/L/yr
- CCarlton County, Minnesota · Water Clarity↑ Improving+1.02 m/yr
- AVilas County, Wisconsin · Water Clarity↑ Improving+2.13 m/yr
- CCarlton County, Minnesota · Water Clarity↑ Improving+0.42 m/yr
- BSt. Louis County, Minnesota · Water Clarity↑ Improving+2.46 m/yr
- FHennepin County, Minnesota · Water Clarity↑ Improving+0.30 m/yr
Most declining
Largest relative decline per year on any single metric.
- CCarver County, Minnesota · Phosphorus↓ Declining+28.66 µg/L/yr
- CCarver County, Minnesota · Phosphorus↓ Declining+28.01 µg/L/yr
- CCarver County, Minnesota · Phosphorus↓ Declining+23.30 µg/L/yr
- CDakota County, Minnesota · Water Clarity↓ Declining-0.77 m/yr
- BIsanti County, Minnesota · Water Clarity↓ Declining-0.80 m/yr
- AIsanti County, Minnesota · Water Clarity↓ Declining-0.72 m/yr
- AIsanti County, Minnesota · Water Clarity↓ Declining-0.72 m/yr
- FScott County, Minnesota · Water Clarity↓ Declining-0.25 m/yr
- BDakota County, Minnesota · Water Clarity↓ Declining-0.92 m/yr
- BIsanti County, Minnesota · Water Clarity↓ Declining-0.73 m/yr
- DIsanti County, Minnesota · Water Clarity↓ Declining-0.72 m/yr
- CMilwaukee County, Wisconsin · Chlorophyll-a↓ Declining+6.87 µg/L/yr
Methodology
- Data: EPA Water Quality Portal — secchi depth, total phosphorus, and chlorophyll-a samples.
- Annual values: median of all samples for that lake in that year.
- Trend fit: linear regression across annual medians; classified improving, declining, or stable when change/year is below 2% of the long-run mean.
- Eligibility: lakes with at least four years of data on the metric being ranked.
- Limitation: the current sample window is short (~2020–2025). Treat trends as direction, not certainty. We will revisit this page as the sample window widens.
Looking for a single lake? Open any Minnesota or Wisconsin lake page and follow the Trends link.