About the data and its limits

Lake Notice republishes state harmful algal bloom advisory records, one page per water, with each water's full history: California's since 2016 and Missouri's since 2017. It adds nothing the states did not record. Where EPA has a satellite estimate for a large lake, it is shown separately and labeled as one.

What the data cannot tell you

Absence of an advisory does not mean a water is safe. Most lakes and rivers are never tested, reports come from the public and partner agencies on a voluntary basis, and the state says its data "is not exhaustive of all ambient conditions across the state."
An advisory is a recommendation. In the state's words, "a recommended advisory may or may not result in a posting of the advisory on the ground." Here, "posted" means published in the state's records.
End dates are often blank. "Advisory 'End Date' can be blank for a long time." A blank end date is unknown, never "ended".
Timing. The pipeline reads the states' data once a day and the satellite estimates once a week. The state's own map is updated daily. Check the official map and posted signs before you go.

How a status is decided

Each report is one spot at a water. For each spot, the latest record that decides anything wins:

An advisory (Caution, Warning, Danger, or another sign type the state uses) means the spot reads "last posted …, no all-clear recorded" until the state records an end.
The state's "None" record (no advisory recommended) or an end date the state recorded ends it, with that date.
"NA - refer to Report Details" and blank levels change nothing.

A water shows an advisory if any of its spots does, at the highest level among them. Rows the pipeline could not place honestly are left out and counted: 267 in the current file (18 Missouri: missing observation date; 205 missing or unreadable advisory date; 44 not linked to a bloom report).

Sources and licenses

Each source records the end of an advisory in its own way, and only an explicit end counts. Official advisories and satellite estimates are separate kinds of record and are never mixed.

California State Water Resources Control Board

What it is: Freshwater and Estuarine Harmful Algal Bloom (FHAB) Program (official advisory records)
Data: https://data.ca.gov/dataset/surface-water-freshwater-harmful-algal-blooms
License: Other (Public Domain); No Restrictions on Public Use (read Oct 12, 2026)
How an end is recorded: An advisory ends only when the state records a later "None" (no advisory recommended) at the same spot, or an end date. A blank end date is unknown.
Last read: hab-responses_2026-10-20.csv (14437 rows), Oct 22, 2026

Advisory data: California State Water Resources Control Board, Freshwater Harmful Algal Bloom Program, via data.ca.gov (public domain). Advisories are recommendations; reporting is voluntary and incomplete.

Missouri Department of Natural Resources

What it is: Harmful Algal Bloom Response (public water bodies) (official advisory records)
Data: https://gis.dnr.mo.gov/host/rest/services/wqm/HAB_SUBMIT_POINTS/MapServer/6
License: State of Missouri Data Policy (https://mo.gov/data-policy); Use permitted with the required disclaimer; revocable by the State (read Oct 12, 2026)
How an end is recorded: An advisory ends only when the department records a dissipation date. A closed case without one is not read as an end.
Last read: HAB_SUBMIT_POINTS layer 6 (public water bodies) (278 rows), Oct 22, 2026

Missouri data: Missouri Department of Natural Resources, Harmful Algal Bloom response map. Status codes are the department's; their plain-English labels here are this site's reading of the codes.

Disclaimer required by the State of Missouri:

The data made available here has been modified for use from its original source, which is the State of Missouri. THE STATE OF MISSOURI MAKES NO REPRESENTATIONS OR WARRANTY AS TO THE COMPLETENESS, ACCURACY, TIMELINESS, OR CONTENT OF ANY DATA MADE AVAILABLE THROUGH THIS SITE. THE STATE OF MISSOURI EXPRESSLY DISCLAIMS ALL WARRANTIES, WHETHER EXPRESS OR IMPLIED, INCLUDING ANY IMPLIED WARRANTIES OF MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE. The data is subject to change as modifications and updates are complete. It is understood that the information contained in the Web feed is being used at one’s own risk.

The publisher's terms let it withdraw permission: “The State of Missouri reserves the right to modify and/or discontinue providing any or all of the data feeds at any time and to require the termination of any and all displaying, distributing or otherwise using any or all of the data for any reason including, without limitation, your violation of any provision of these Terms of Use.” If it does, this site removes that state's data.

U.S. Environmental Protection Agency

What it is: Cyanobacteria Assessment Network (CyAN), Sentinel-3 OLCI weekly composite (satellite estimate)
Data: https://www.epa.gov/water-research/cyanobacteria-assessment-network-cyan
License: U.S. Government work (public domain under 17 U.S.C. § 105); no license is stated on the CyANWeb API; EPA calls CyANWeb experimental and provisional, a research-level tool (read Oct 12, 2026)
How an end is recorded: A satellite estimate is never an advisory and never ends one. It measures how much cyanobacteria there is, not toxins.

Satellite estimates: U.S. EPA Cyanobacteria Assessment Network (CyAN), from Copernicus Sentinel-3 data. Provisional, research-level estimates; EPA does not endorse this site.

About the satellite estimates

This is a satellite estimate from the U.S. EPA's Cyanobacteria Assessment Network, not an advisory. It estimates how much cyanobacteria is in the water near the lake's center, not whether toxins are present: a high number does not mean toxins, and a low one does not mean there are none. It covers lakes of about 1 square kilometer and larger, so small ponds, dog parks and most rivers are not covered, and clouds can hide a lake for weeks. It never changes the advisory status above.

The iPhone app

A paid iPhone app is in development. Browsing and every lake's history will be free; alerts for your favorite lakes and a Home Screen widget will be a one-time purchase. The app checks this site's data file about once a day, so an alert comes within about a day of the state publishing a new advisory, not in real time.