Blue-Green Algae in Illinois Lakes

Blue-green algae advisories in Illinois are issued and lifted by Illinois Environmental Protection Agency with the Department of Public Health, and a bloom can move across a lake on the wind inside an afternoon, so the current answer is theirs: Illinois EPA Algal Bloom Dashboard carries the agency’s dashboard of confirmed algal blooms and the bloom report form behind it. EPA draws the same line: "State, Tribal and local governments may issue advisories for water bodies with HABs." This page gives you who owns the question here, what it takes to get a waterbody posted, and the link to today's status.

At Illinois EPA Algal Bloom Dashboard, which carries the agency’s dashboard of confirmed algal blooms and the bloom report form behind it. EPA’s federal directory labels the Illinois entries as Department of Public Health pages, but both addresses it gives are Illinois EPA pages and one no longer resolves. The dashboard address above is the agency’s own and answered on 2026-09-03. The sign at the access point outranks any website, including that one, because somebody put it there after looking at that specific water. CDC's own advice is to "Check for and follow swimming, fishing, and shellfish advisories" and to "Stay out of discolored, scummy, or smelly water and keep pets away"

No, and this is the most important sentence on this page. Arkansas DEQ puts it plainly: "A water body with no HAB advisory is not an indication that a bloom is not present. Blooms are unpredictable. They can develop rapidly and may move across a water body due to wind or water current. If you suspect that a water body is experiencing a harmful algal bloom, it is best to avoid." An absent advisory can mean the lake was sampled and the result was under the state threshold, or that nobody has sampled that lake this year, or that the sample predates the calm hot week that just built the bloom. Even in a state that publishes a current list, the list covers the waterbodies the programme monitors, not every lake in Illinois.

EPA compiles every state's numbers, and for Illinois it records a single tier recreational value for microcystins of EPA's own recommended criterion, which is 8 micrograms per litre. Those are EPA's records of Illinois's decisions, not thresholds of ours, and a threshold is not a status: it is what it takes to get a waterbody posted, and says nothing about whether anything is posted today.

CDC: "Harmful algal blooms can look like foam, scum, mats, or paint on the surface of the water. They can also grow underneath the water, making some harmful algal blooms hard to see." EPA adds the detail that catches people out, which is that the danger outlasts the visible bloom: "Microcystis is the most common bloom-forming genus. Its blooms resemble a greenish, thick, paint-like (sometimes granular) material that accumulates along shores. Scums that dry on the shores of lakes may contain high concentrations of microcystin for several months, allowing toxins to dissolve in the water even when the cells are no longer alive or after a recently collapsed bloom." Illinois Environmental Protection Agency puts the local version this way: "The safest thing to do is to treat every algal bloom as if it could be dangerous."

Yes, and every state programme in the country says so. CDC: "Contact a veterinarian immediately if your pets or livestock seem sick after going in or near water. Animals can get very sick or even die within hours of coming into contact with harmful algae or cyanobacteria." A dog wades the shallow downwind edge where the scum concentrates, drinks the water, then licks its coat, which is three exposure routes a swimmer does not have. Two states, Indiana and Oregon, publish separate and far lower cyanotoxin values for dogs; most do not, which is a gap rather than an all clear. If an animal is sick after being in or near water, CDC says to contact a veterinarian immediately.

Illinois Environmental Protection Agency with the Department of Public Health, through the reporting route on Illinois EPA Algal Bloom Dashboard. In most states a bloom becomes known because somebody reported it rather than because a sampling schedule found it, which is why the reporting form is usually the most prominent thing on a state HAB page. For a person with symptoms, CDC says: "If you think you have symptoms caused by a harmful algal bloom, contact a healthcare provider or the Poison Control hotline at 1-800-222-1222." For an animal, a veterinarian, straight away. Reports reach the agency through that route, not through this page.

No, three separate things with three separate lab tests. EPA: "Several different types of algae can produce toxic HABs. The most common algae associated with marine toxic HABs include the dinoflagellates (e.g., Florida red tide Karenia brevis) and diatoms (Pseudo-nitzschia) while those most associated with freshwaters are dominated by cyanobacteria (e.g., Microcystis)." Red tide is marine, caused by Karenia brevis and monitored by different agencies, and our red tide pages cover it. A beach advisory at a coastal or Great Lakes beach is usually about fecal indicator bacteria under the BEACH Act, which our beach water pages cover. A bacteria result says nothing about cyanotoxins and a cyanotoxin result says nothing about bacteria.

From EPA's compilation of state and Tribal cyanotoxin thresholds, which EPA describes as "This page offers a compilation of the cyanotoxins thresholds used by state and Tribal programs to make advisory decisions for drinking water and recreational uses." We read its 146 rows on 2026-09-03, as the page stood after its July 13, 2026 update, and stored them unchanged; a US Government work in the public domain. EPA's federal directory link for Illinois no longer resolves cleanly, and the note above the link on this page says where it lands now. Every figure on this page is EPA's.