Blue-Green Algae in Delaware Lakes

Blue-green algae advisories in Delaware are issued and lifted by Delaware Department of Natural Resources and Environmental Control, and a bloom can move across a lake on the wind inside an afternoon, so the current answer is theirs: Blue-Green Algae in Delaware carries the department’s blue-green algae guidance and the recreational water monitoring programme it sits inside. 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 Blue-Green Algae in Delaware, which carries the department’s blue-green algae guidance and the recreational water monitoring programme it sits inside. EPA’s federal directory sends Delaware to a DNREC red tide page and a health department cyanobacteria PDF rather than to the state’s blue-green algae page. The address above is the current DNREC page, found and opened 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. Delaware publishes no single statewide list at all, so the absence of a listing is not even the absence of a report.

Nothing, as far as EPA can tell. EPA's compilation of state and Tribal toxin thresholds, updated July 13, 2026, records no recreational cyanotoxin threshold for Delaware. That does not mean Delaware ignores blooms; Delaware Department of Natural Resources and Environmental Control runs a programme and it appears on this page. It means the decision to post rests on visual assessment, cell counts or professional judgement rather than on a published concentration, so there is no number to compare against another state's.

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." Delaware Department of Natural Resources and Environmental Control publishes Delaware specific identification guidance on the page linked above.

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.

Delaware Department of Natural Resources and Environmental Control, through the reporting route on Blue-Green Algae in Delaware. 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 Delaware 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.