Lake Algae Advisories, State by State

Current advisories are published by each state programme, and every state page here links the page where that state posts its own current status, each link verified on 2026-09-03. Cyanobacteria advisories are issued and lifted within days and a bloom moves across a lake on the wind inside an afternoon, which is why the state's own page is the current answer. EPA is equally direct about whose decision it is: "State, Tribal and local governments may issue advisories for water bodies with HABs."

Three different organisms, three different laws and three different 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)." The legal split follows the biology: "Under the Harmful Algal Bloom and Hypoxia Research and Control Act (HABHRCA), the National Oceanic and Atmospheric Administration (NOAA) is primarily responsible for estuarine, marine, and Great Lake waterbodies, whereas the EPA bears primary responsibility for all other freshwaters." So freshwater cyanobacteria in lakes and reservoirs is EPA's and the states', marine red tide and the Great Lakes are NOAA's, and fecal indicator bacteria at coastal and Great Lakes beaches is the BEACH Act, a fourth thing again. A clean bacteria result says nothing whatever about cyanotoxins.

45 of the 50. Of those, 29 publish current per waterbody advisory status as a list, table, map or dashboard; 8 publish verified public bloom reports on a map and say in their own words that the map is a record of what was reported rather than a survey; and 8 publish the programme, the guidance and the reporting route while the advisory decision itself is made locally. The remaining 5 states are named on this page with the specific reason each one is missing. None of those reasons is that the state has no blooms: CDC states that harmful algal blooms "have been reported in all 50 states, Puerto Rico, and the U.S. Virgin Islands."

It depends entirely on the state, which is the single most surprising thing about this subject. EPA's own recommendation is 8 micrograms per litre of microcystins and 15 of cylindrospermopsin for recreational water: "In 2019, the EPA issued final recommended recreational ambient water quality criteria or swimming advisories for two cyanotoxins, microcystins and cylindrospermopsin. The agency has identified recommended concentrations of these cyanotoxins at or below which human health is protected while swimming or participating in other recreational activities in and on the water." But adoption is optional. "States, territories, and authorized Tribes can consider adopting these recommended criteria into their water quality standards and using them for CWA purposes. Alternatively, they can use these values as the basis of swimming advisories for public notification purposes at recreational waters." 32 of the 45 states here publish a recreational threshold and 13 publish none at all, and among those that do the range runs from New Mexico watching above 0.1 micrograms per litre to states whose danger value is 2000.

Because a dog does three things a swimmer does not. It wades the shallow downwind edge where wind and current pile the scum up, it drinks the water, and then it licks the residue off its coat. CDC states it plainly: "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." Only two states in EPA's compilation, Indiana and Oregon, publish separate and much lower cyanotoxin values specifically for dogs. That is a gap in the numbers rather than evidence that dogs are safe elsewhere, and every state programme here carries an animal warning of some kind.

No, and no state programme claims otherwise. Minnesota Pollution Control Agency: "Blue-green algae blooms are harmful when they produce toxins that can make humans and animals sick. Most blooms are not harmful. You can’t tell by looking at a bloom if it is harmful or not." Connecticut DEEP: "It is important to note that not all algal blooms are harmful algae blooms (HABs), however it is not possible to determine the level of toxins in the water without a more detailed evaluation. Out of precaution it is best to avoid direct contact with water experiencing a bloom." Toxin production turns on and off within a bloom, so the same lake can be dangerous on Tuesday and not on Thursday with no visible change. What you can see is whether there is a bloom at all, and CDC's rule follows from that: "Stay out of discolored, scummy, or smelly water and keep pets away."

Not necessarily, and this is the detail that catches people out most often. EPA: "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." So a shoreline that looked bad last week and looks clear today can still carry dried scum that a dog will investigate, and the toxin can dissolve back into the water from cells that are already dead. This is also why a photograph of a lake, including a recent one, is not evidence of anything.

No. The three shapes on this page describe how a state has organised publication, not how well it protects anybody: several states that publish no statewide list have stricter thresholds than several that do, and a state with more listed waterbodies may simply sample more. Turning EPA's compilation into a league table would be inventing a fact.

EPA runs CyAN, which turns satellite imagery into cyanobacteria estimates for around 2,000 large US lakes and publishes them on EPA's own portal; the portal does not allow cross origin reads, so its estimates live on EPA's site rather than here. What EPA also publishes, and this site carries, is durable: "As part of its efforts to protect public health, the EPA compiles and displays recreational and drinking HAB occurrence and/or advisory data publicly reported by states on a monthly basis."

Two EPA pages, read directly at build time and stored as a committed snapshot: EPA's compilation of state and Tribal toxin thresholds, 146 rows including 7 Tribal nations, last updated July 13, 2026; and EPA's State and Tribal HAB Programs directory, last updated July 15, 2026. Both are US Government works in the public domain. Every state programme link on this site was verified in a browser on 2026-09-03, and 16 of the 45 state pages carry a note on where EPA's own federal directory link for that state lands now, because a surprising number of those are stale.