What does a harmful algal bloom look like?

Pea-soup green or blue-green water, paint-like surface streaks, scum or foam mats along the shoreline, and a dried crust on rocks and banks. Not all blooms are visible, and toxicity cannot be judged by eye.

What do I do if my dog swam in water with algae?

Rinse the dog with clean water immediately, before it can lick its coat, and do not let it drink the pond water. If it shows vomiting, weakness, staggering, tremors or seizures, go to a vet immediately — cyanotoxin poisoning can be fatal within hours.

Pond safety

Can my dog swim in a Delaware pond?

Not without looking first. Blue-green algae blooms peak in Delaware millponds in August and September, and the toxins can kill a dog within hours. If the water is scummy, pea-green, or has foam or mats along the edge, keep the dog out of it.

Why this is a Delaware problem specifically

Nearly every freshwater spot a dog swims in this state is a millpond — warm, shallow, slow-moving and nutrient-rich. Those are precisely the conditions that produce cyanobacteria blooms, and the season runs through August and September.

Dogs are far more exposed than people are. They drink while they swim, and then they lick their coat dry afterwards. A dog can take in a meaningful dose from water a person would only wade in.Not all cyanobacteria are toxic, and there is no way to tell by looking. Treat any bloom as if it is.

What a bloom looks like

Pea-soup green, blue-green, or brownish water
Paint-like streaks on the surface
Scum, mats, or foam collecting along the downwind shoreline
A dried crust on rocks or the bank — still toxic, and dogs lick it
An unusual musty or septic smell

Some blooms aren't visible at all. Clear-looking water is not a guarantee — it just means there's nothing obvious to see.

The ponds to be careful about

Not a warning that any of these is blooming today — we don't track that and neither should you take our word for it. These are simply the freshwater bodies where Delaware dogs actually swim.

Lums Pond
Bear. The one with the off-leash area, and the one dogs actually swim in.
Trap Pond
Laurel. Bald cypress, warm and slow.
Killens Pond
Felton.
Records Pond
Laurel.
Chipman Pond
Laurel.
Wagamon Pond
Milton.

Lums Pond deserves its own paragraph

It is the highest-rated dog spot in the state, and the reason people love it is that dogs can swim in the pond. Its reviews are full of that. None of them mention blooms. It is a millpond like the others, and if the water looks wrong on the day you visit, the swimming is the part to skip — the off-leash area is still worth the trip.The other thing to know about Lums Pond is that it isn't fenced.

If your dog has been in the water

Rinse it with clean water immediately, before it starts licking its coat. Carry a jug in the car in bloom season.
Don't let it drink pond water — bring fresh water and a bowl.
Watch it closely for the rest of the day. Onset can be fast.

Signs to drive to a vet for

Vomiting or bloody diarrhoea
Weakness, staggering, or collapse
Muscle tremors or seizures
Excessive drooling
Difficulty breathing

Who actually monitors this

We deliberately do not publish a bloom map or a "safe today" badge. Conditions change within hours, a stale green light is more dangerous than no light at all, and these are the agencies that sample the water:

DNREC — Delaware's environmental agency, for current advisories and closures.
Delaware Division of Public Health— publishes a cyanobacteria FAQ and health guidance.
CDC— preventing pet illness from harmful algal blooms.