Updated April 2026 · EPA Water Quality Portal & WI DNR
Lake Water Quality Blog
Data-driven articles on lake water quality, swimming safety, and what the science says about your favorite lakes in Minnesota and Wisconsin. Built from EPA Water Quality Portal records, Wisconsin DNR Fisheries survey reports, and Minnesota DNR LakeFinder attributes.
What the LakeQuality Blog Covers
Lake water quality data is rich in both Minnesota and Wisconsin — between MPCA, WI DNR, USGS, and citizen monitoring programs, the EPA Water Quality Portal aggregates millions of measurements across roughly 27,000 monitored lakes. That depth supports questions you cannot answer at the level of a single lake report card: do deeper lakes really have cleaner water, and by how much? Which lakes have improved most over the past decade, and what changed? How widely have zebra mussels spread, and which counties are next in line?
The blog organizes coverage into three threads: data analysis (cross-lake patterns), rankings (top and bottom of the dataset on a specific metric), and guides (first-time readers learning to interpret the grades). Articles are dated, cite their underlying datasets, and are re-checked against EPA WQP and DNR releases on each refresh cycle.
Analysis
Data analysis using EPA Water Quality Portal records and DNR LakeFinder attributes — looking for patterns across thousands of lakes that no single lake report card surfaces.
Do Deeper Lakes Have Better Water Quality?, Data Analysis
We analyzed 2,800+ lakes to find the relationship between lake depth and water quality grades. The answer is clear, and the reasons are fascinating.
Lakes That Made the Biggest Comeback, Improving Water Quality
Which lakes went from poor to excellent? Data-driven analysis of the biggest water quality success stories in Minnesota and Wisconsin.
Zebra Mussel Spread: How Many Lakes Are Affected?
Data analysis of zebra mussel infestations across the region. Which counties are hit hardest and what boaters need to know.
Which Lakes Have the Most Fish Species?
Analysis of fish species diversity across 2,700+ lakes. What makes a lake a biodiversity hotspot for fish?
Ranking
Ranked tables drawn directly from EPA monitoring data and DNR records — not editorial picks, not tourism marketing.
The Clearest Lake in Every County, MN & WI
For each of 144 counties, the single lake with the best water clarity. Some have 30+ feet of visibility. Others barely reach 4 feet.
Best Lakes for Swimming in Minnesota & Wisconsin (2026)
The top 15 lakes with the best water quality grades for safe swimming. Ranked by clarity, phosphorus levels, and algae risk using EPA monitoring data.
Lakes with the Worst Water Quality in the Midwest (2026)
The 15 lakes with the lowest water quality grades in Minnesota and Wisconsin. What causes poor grades and what it means for lake health.
Guide
How-to coverage for first-time lake report card readers — what each measurement means, how the grades are derived, and how to use them.
How These Articles Are Researched
Every grade, ranking, and trend in these articles links back to a public dataset. Water quality measurements come from the EPA Water Quality Portal. Fisheries data comes from Wisconsin DNR survey reports. Lake physical attributes come from the Minnesota DNR LakeFinder. Read the full LakeQuality methodology for the join logic, scoring weights, and refresh cadence.
Frequently Asked Questions
How are these articles researched?
Each article runs on the same dataset that powers the rest of LakeQuality: EPA Water Quality Portal monitoring records, Minnesota Pollution Control Agency lake reports, Wisconsin Department of Natural Resources lake reports and fisheries surveys, and U.S. Geological Survey records, joined to Minnesota DNR LakeFinder physical attributes. We do not estimate or model — every claim links to an underlying public dataset. Last refreshed April 2026.
Why focus on Minnesota and Wisconsin?
Both states have unusually rich public lake monitoring programs. Minnesota tracks roughly 12,000 lakes through MPCA and the Citizen Lake Monitoring Program; Wisconsin tracks approximately 15,000 through WI DNR programs including the Citizen Lake Monitoring Network. The combination of dense monitoring, public DNR data portals, and 681 Wisconsin DNR Fisheries Survey reports gives a richer picture than is possible in most other states. The articles use that depth.
How often is the data updated?
EPA Water Quality Portal records refresh as state agencies upload new monitoring data — most commonly on a 6-12 month cycle. LakeQuality re-runs every grade and ranking against the new file when each refresh ships. The master refresh date is April 2026.
Are these grades a substitute for current swim safety advisories?
No. Grades reflect long-term summer-season water quality. Day-of conditions can change quickly — a heavy rain can flush sediment and bacteria into a lake, and warm calm weather can trigger localized cyanobacteria (blue-green algae) blooms even in A-graded lakes. Always check the Minnesota Department of Health's current advisory list and the Wisconsin Department of Natural Resources' beach advisory page before swimming, especially with young children, pregnant family members, or pets.
Where can I get the underlying data myself?
Every dataset cited here is publicly available. The EPA Water Quality Portal at waterqualitydata.us provides direct download access to all monitoring records. The Minnesota DNR LakeFinder publishes lake physical attributes. The Wisconsin DNR publishes fisheries survey reports through its lake records portal. Each article ends with a citations block listing the specific data source for that piece.
Sources: EPA Water Quality Portal, Minnesota Pollution Control Agency, Wisconsin DNR Fisheries, U.S. Geological Survey, EPA STORET, Minnesota DNR LakeFinder. All data is government public domain. Cite as: "LakeQuality, April 2026 reading. Data: EPA WQP & WI DNR."
Last updated 2026-04-08 · 8 articles published.