Updated July 2026 · EPA Water Quality Portal & WI DNR
Lake Water Quality Articles
Data-driven articles on lake water quality, swimming safety, and what the science says about your favorite lakes. Built from EPA Water Quality Portal records, Wisconsin DNR Fisheries survey reports, and Minnesota DNR LakeFinder attributes.
What the LakeQuality Articles Cover
Lake water quality data is rich across the 12 states we cover — between state agencies like MPCA and WI DNR, USGS, and citizen monitoring programs, the EPA Water Quality Portal aggregates millions of measurements across tens of thousands of monitored lakes in those states. 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 articles organize 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.
Algae Season 2026: Which States and Lakes Carry the Most Advisories
Where harmful-algae risk concentrates this summer, by nutrient impairment and elevated algae signals across the 12 states we track.
The State of America's Lakes 2026
A data snapshot of 6,000+ monitored lakes across 12 states: grade distribution, the clearest and greenest states, and what's improving.
The Lakes Where Water Quality Is Slipping
The lakes showing the steepest multi-year declines in clarity and rising nutrients, based on trend data, and what's driving the drop.
Fishing Opener 2026: What the Water Data Shows
Water temperature and level readings from USGS gauges heading into the 2026 fishing opener, and what they mean for early-season fishing.
Ice-Out 2026: When Minnesota Lakes Actually Thawed
The 2026 ice-out dates for Minnesota lakes versus their long-term medians, using DNR ice records.
Do Deeper Lakes Have Better Water Quality?, Data Analysis
We analyzed every lake with depth data (currently Minnesota and Wisconsin) 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 across the U.S.
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 lakes in states with DNR fish-survey data (Minnesota, Wisconsin, Michigan). 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.
Summer 2026: The Cleanest Lakes to Swim Right Now
The best-graded lakes for swimming this summer, ranked by clarity and low algae, plus what to check the day you go.
The Cleanest Lakes in Every State We Track
The top-graded lakes in each of the 12 states we cover, ranked by water clarity, phosphorus, and algae.
The Clearest Lake in Every County We Track
For every county we track, the single lake with the best water clarity. Some have 30+ feet of visibility. Others barely reach 4 feet.
Best Lakes for Swimming Across 12 States (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 U.S. (2026)
The 15 lakes with the lowest water quality grades across the U.S. 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.
What to Check Before Buying Lakefront Property
A water-quality due-diligence checklist for lakefront buyers: clarity trend, nutrient impairment, algae history, invasive species, and depth.
How to Choose a Clean Lake for a Cabin or Weekend Trip
A five-check framework for picking a lake with good water quality: clarity, phosphorus, algae history, depth, and trend.
Trophic State Explained: Why Some Lakes Are Blue and Others Pea-Green
What oligotrophic, mesotrophic, eutrophic, and hypereutrophic mean, how the Carlson Trophic State Index works, and what each means for recreation.
Why Lakes Turn Green: How Phosphorus and Nutrient Pollution Work
How excess phosphorus fertilizes algae and turns lakes green, where the nutrients come from, and what it means for a lake's grade.
Mercury, PFAS, and the Fish You Shouldn't Eat
Why states issue fish-consumption advisories, which contaminants (mercury, PCBs, PFAS) drive them, and how to eat lake fish more safely.
Is It Safe to Swim? How E. coli and Beach Advisories Work
What swim advisories mean, how E. coli monitoring works, and when a lake's long-term grade is and isn't a swim-safety guide.
Algae Blooms Explained: When Green Water Is Dangerous
How to tell a harmless algae bloom from toxic cyanobacteria, the health risks for people and pets, and where to check advisories.
Water Clarity Explained: What a Secchi Depth Reading Tells You
What a Secchi reading measures, what counts as good water clarity, and why clear water is not always clean.
Lake Water Quality Grades Explained: What A-F Means
How we grade every lake from A to F using secchi depth, phosphorus, and chlorophyll-a measurements. Understand what each grade means for swimming and recreation.
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 July 2026.
Which states does LakeQuality cover?
LakeQuality grades lakes across 12 states: Minnesota, Wisconsin, Illinois, Michigan, Iowa, Ohio, Pennsylvania, New York, Missouri, Indiana, North Dakota, and South Dakota. Minnesota and Wisconsin carry the deepest supplemental datasets — lake depth, fish surveys (including 681 Wisconsin DNR Fisheries Survey reports), and Minnesota ice-out records — because MPCA and WI DNR run two of the richest public lake monitoring programs in the country. The articles draw on the full 12-state dataset, and lean on the Minnesota and Wisconsin depth where a question demands those extra attributes.
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 July 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 (aggregating monitoring agencies in every covered state), 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, July 2026 reading. Data: EPA Water Quality Portal (all covered states)."
Last updated 2026-07-05 · 23 articles published. Article photos are Creative Commons / public-domain images, credited on each article.