Frequently Asked Questions

PlainLakes compiles records from two official federal systems: EPA ATTAINS, which holds the water-quality assessment decisions that states and tribal nations report under Clean Water Act sections 303(d) and 305(b), and the USGS National Water Information System (NWIS), which provides daily lake and reservoir water-level observations. No other sources are used, and no values are modified.

It is the reporting government's regulatory finding that the waterbody does not meet the water-quality standard for a designated use, such as recreation, aquatic life, or fish consumption. A lake can support some uses and not others, so each use gets its own verdict. Lakes not supporting a use are typically listed as impaired for that use.

The government that reports the waterbody to EPA. For most lakes that is the state environmental agency, but ATTAINS is not a state-only register: under section 518 of the Clean Water Act, EPA can approve a federally recognized tribe for treatment in a similar manner as a state, and a tribe with that approval sets water-quality standards for waters under its jurisdiction, assesses them, and files its own Integrated Report. Those verdicts are the tribe's own, and the state whose borders the water sits inside did not make them. Every PlainLakes page names the government that filed the record it shows.

Section 303(d) of the Clean Water Act requires each state, and each tribal nation approved to administer the program for its own waters, to list waterbodies that are impaired and still need a cleanup plan, known as a Total Maximum Daily Load. Those lists are submitted to EPA on reporting cycles that are typically every 2 years. PlainLakes shows the assessment decisions behind those listings as recorded in EPA ATTAINS.

It is the specific problem the reporting agency named when it found a waterbody impaired, for example mercury, nutrients, pathogens, or low dissolved oxygen. A single lake can have several impairment causes affecting different designated uses. The causes shown on PlainLakes come directly from that agency's report in EPA ATTAINS.

PlainLakes shows the reported fish-consumption use status, which is a starting point, not advice on what is safe to eat. A fish advisory program publishes the actual guidance: which species to limit, how many meals per month, and stricter limits for children and pregnant women. That program is run by your state health or environmental agency, and by the tribal government where the waters are under its jurisdiction. Always check the applicable advisory before eating fish from any lake.

An assessment status is a regulatory finding reported to EPA, often on a 2-year cycle, about whether a waterbody meets water-quality standards. A fish advisory is consumption guidance issued by a state health or environmental agency, or by a tribal government for waters under its jurisdiction, and it is more specific and usually more current, covering individual species and sensitive groups. When the two seem to disagree, follow the advisory.

Reporting agencies assess a subset of their waters each reporting cycle, so many lakes have never been assessed and reported to EPA. PlainLakes covers the lake-type waterbodies that a state or tribal government has reported to EPA ATTAINS under the Clean Water Act from the 50 states and the District of Columbia. That register is the whole corpus: it is not a census of every lake in the United States. USGS water-level records are matched onto waterbodies that are already in that register, so a gauge adds a water level to a lake PlainLakes covers — it never adds the lake. A lake that USGS monitors but no agency has reported to EPA does not appear here. ATTAINS also carries assessment units an agency has retired — closed permanently, usually because the water was re-divided into new units assessed in its place. Every total on this site counts the current register only, because a retired unit and the units that replaced it would otherwise count the same water twice. Retired units keep their pages, which say so, and each state page reports how many it has. If a lake is missing, no agency has reported it to EPA for this cycle. If it appears without an assessment status, it was reported but not assessed. Neither means its water is clean or polluted — an unassessed lake is simply one nobody has judged.

Water-level records come from USGS NWIS and cover the trailing 365 days of daily observations at lakes with an active gage. PlainLakes ingests them as daily-batch snapshots, never real-time. USGS marks each daily value approved for publication or provisional, and review runs months behind collection, so the latest reading on every gauge record this site publishes is provisional and subject to revision by USGS. Each record names the date USGS has approved that gauge through. For live conditions, check the USGS site for that gage directly.

Reporting agencies submit assessment decisions to EPA on cycles that are typically every 2 years, and some lag behind that schedule. PlainLakes refreshes its database as new submissions appear in ATTAINS, and each page shows the reporting cycle its verdicts come from. Water levels update on a separate daily-batch schedule.

Yes, PlainLakes is completely free. All data comes from publicly available federal records in EPA ATTAINS and USGS NWIS. No registration, subscription, or payment is required.

Verdicts and readings are loaded directly from EPA ATTAINS and USGS NWIS without modification, so pages are as accurate as the official records. The main caveats are lag, since assessment cycles are typically 2 years, and provisional recent USGS values. For decisions that matter, verify against the source records at epa.gov/waterdata/attains and waterdata.usgs.gov/nwis.

Email corrections@plainlakes.com with the lake page URL, the specific value that looks wrong, and the official source you are comparing against. PlainLakes checks the report against the cited source records and, if the error is on this side, fixes it in the database so every affected page is corrected. See the contact page for details.