About LakeQuality
The water, as the agencies measured it.
What we do
US lake pages carry EPA and state agency measurements. Ontario and Québec are listed with provincial measurements. 38 country hubs publish official ratings, attributed to the agency that issued them. LakeQuality shows the nutrient and algae measurements a state or federal agency published for each lake, so swimmers and anglers can see what the monitoring record actually says. Each US reading is shown beside the condition class EPA assigns to it for the lake's own ecoregion, because what counts as clean water in the Nebraska Sand Hills is not what counts as clean water in the Sierra Nevada. Where the record holds no nutrient or algae reading, the page shows what it does hold and says so rather than guess.
We focus on U.S. lake and freshwater quality. Every page on lakequality.org is built from the EPA Water Quality Portal, the Minnesota DNR LakeFinder, and the Wisconsin DNR Surface Water dataset, cited and linkable so readers can trace any number back to its source.
Who runs this
LakeQuality is built and maintained by the Lake Quality Team. We're a small group working on making public U.S. lake and freshwater quality data easier for non-specialists to read. If you have a correction, a data tip, or a question about how a number was derived, the contact email below reaches us directly.
Who this is for
LakeQuality is built for swimmers, anglers, cabin owners, lake-association members, public-health staff, and state environmental agencies.
Why this exists
Public data on U.S. lake and freshwater quality is technically free, but practically locked behind file formats, acronyms, and paywalled dashboards. LakeQualityexists to close that gap: take the raw federal and public-sector data, and turn it into pages a normal person can read in thirty seconds.
How we work
- Primary source only. We pull from the EPA Water Quality Portal, the Minnesota DNR LakeFinder, and the Wisconsin DNR Surface Water dataset and cite the exact dataset and version on every page.
- No invented numbers. If a figure is not in the underlying public data, it does not appear on lakequality.org. We never generate synthetic statistics to fill gaps.
- Methodology, in plain English. We take EPA Water Quality Portal samples from the June-September index period, chlorophyll-a, total phosphorus, total nitrogen, turbidity, true colour and Secchi depth, and show each lake's median readings beside the condition class EPA publishes for its ecoregion in the National Lakes Assessment 2022 Technical Support Document (EPA 841-R-24-006, Table 6-3). Those classes are set at the 75th and 95th percentiles of least-disturbed reference lakes within each ecoregion, so a lake is compared with its own regional peers rather than a national average. Chlorophyll-a is the most direct indicator because it measures algal biomass; phosphorus and nitrogen are the nutrients that feed it. Water clarity carries no class, because EPA assigns none to Secchi depth and low clarity is either redundant with chlorophyll-a or caused by natural dissolved colour or suspended sediment; we show clarity in feet and explain what drives it. The full cutpoint table and the sampling floors are on our methodology page.
- Refreshed on a schedule. Refreshed every four months as new state-agency samples are pushed to the EPA Water Quality Portal. Ice-out observations, fish-species records, and invasive-species listings refresh on the cadence each state’s DNR publishes them, typically annually for ice data and quarterly for invasive-waters updates.
- Corrections welcome. Readers flag issues all the time. When the source fixes a record, LakeQuality follows.
Known limitations
Most lakes have never been sampled for nutrients or algae, or not recently enough to count. Their pages show what the record holds and say so; that is EPA Integrated Reporting Category 3, insufficient information, a statement about the record and not a finding about the lake. Every page shows the sample counts behind its readings, and only well-sampled lakes enter the cleanest and clearest rankings. The readings cover nutrients and algae. They do not cover E. coli, cyanotoxins, mercury, PFAS or other contaminants, so no reading is a swimming or fish-consumption clearance; whether a lake is safe to swim in or its fish safe to eat is a call for the state water agency and the county health department, and every page links to them. Ecoregion boundaries are a classification, not a wall: two lakes with similar chemistry on opposite sides of one can fall in different EPA classes. Sample timing matters, and depth figures marked as estimates are model output rather than survey measurements.
Why the EPA class, and why clarity is not one of them
Someone deciding where to take their kids swimming does not want to weigh a Carlson TSI of 47 against 53. They want to know whether this lake runs clean for its region, and the EPA National Lakes Assessment condition class answers exactly that: it is set per ecoregion from the 75th and 95th percentiles of least-disturbed reference lakes, so a reading is Good, Fair or Poor relative to the lakes it would naturally resemble.
That regional framing is the point. Reference phosphorus varies roughly thirtyfold across US ecoregions, and the naturally hypereutrophic lakes of the Nebraska Sand Hills would look degraded on any national scale while being exactly as EPA expects them to be.
Water clarity deliberately carries no class. EPA assigns condition classes to phosphorus, nitrogen, chlorophyll-a and turbidity, and none to Secchi depth, because low clarity is either redundant with chlorophyll-a (the water is dark because of algae) or misleading (it is dark because of natural dissolved colour, or because clay is suspended in it). Classifying clarity would mean marking down bog lakes and clay-bottomed reservoirs for being what they naturally are. We show clarity on every page in feet and explain what is driving it instead.
Each page also shows how many samples over how many years support each reading, and where the record holds no nutrient or algae reading, the page says so.
What this data can and cannot tell you
A lake's readings are a few specific measurements taken on a few specific days in a specific season. They are good for the things they are good for and silent on the things they are silent on.
What the readings do well: they identify which lakes in your county or state have persistent nutrient-loading or algal-growth problems versus which are running clean, and how clear the water usually is. If you are choosing a cabin to rent, a lake to fish, or a beach to swim at, they are a defensible starting point.
What the readings do not capture: short-term blooms that happen between sample dates, contamination events from upstream sources that flushed before the last sample window, fish-consumption advisories tied to mercury or PFAS (those live on state “safe to eat” pages and are surfaced separately on our site), beach-specific E. coli spikes (those are tracked in real time by state beach programs, not annual sampling), and invasive-species impacts beyond the binary “documented” flag.
If you are making a decision where any of those matter, a swim with small kids during a hot week, a fishing trip in a county with a recent fish-advisory update, or a property purchase, the readings are one input, not the entire picture. Whether the water is safe today is a call for the state water agency and the county health department, and we link to the upstream state and federal sources on every page so you can check without us in the loop.
How a public record becomes a lake page
The measurements are public. EPA's Water Quality Portal holds samples from state, tribal, and federal agencies. Minnesota DNR LakeFinder and Wisconsin DNR Surface Water add the detail those two states keep in their own systems. A single lake can appear under different spellings in each source, and the raw files are keyed on station codes rather than lake names. Each LakeQuality page matches those records to one lake, names the organization that took each sample, and shows the readings beside the EPA class for the lake's region, so you can read the record without assembling the files yourself.
Independence
LakeQuality is an independent publication. We are not funded, owned, or directed by any of the agencies, companies, or organizations that appear in our data. The site is free to read and is supported by display advertising; advertising is served by third parties and is kept separate from our editorial and data decisions — see our Privacy Policy for how data and advertising cookies are handled. and we do not take paid placements, sponsored rankings, or “remove-my-entry” fees.
Editorial standards
We hold every page to a stated, repeatable process rather than asking readers to take our word for it. How our content is produced and the standards behind it are documented in our Editorial Policy; how we verify figures before publishing is in our Fact-Checking Policy; and how we handle mistakes is in our Corrections Policy.
History
LakeQuality launched in 2025 as part of a small portfolio of independent public-data sites. It has been maintained and updated continuously since.
Contact
Tips, corrections, data-partnership questions, and press inquiries: hello@lakequality.org. More options on our contact page.