Blue-green algae and dogs: lake risks and what to do

What cyanobacterial blooms are

Cornell describes harmful algal blooms as overgrowths of cyanobacteria, favoured by warm weather, dry spells and stagnant water. They may look like scum, foam, mats or blue-green or red-brown patches, like paint on the surface or like pea soup. Appearance cannot distinguish a toxic bloom from a harmless one.

A bloom can also sink or die off and become invisible while the water stays contaminated: the Merck Veterinary Manual notes that toxin is released when algal cells break down. Cornell therefore advises avoiding lakes and ponds where a bloom was reported in the previous 3–4 weeks. Besides lakes and ponds, plant containers, birdbaths and fountains can also harbour cyanobacteria.123

Why the risk is high for dogs

A review of canine poisonings in the United States explains that dogs are particularly vulnerable because they tend to swim in and drink contaminated water during blooms, or eat algal mats. According to Merck, depending on bloom density and toxin content, a small amount of water may be enough.

The main toxins fall into two groups: microcystins damage the liver, anatoxins the nervous system. With neurotoxins, signs can appear almost immediately: tremors, seizures, paralysis, breathing difficulty. Liver toxins cause vomiting, diarrhoea, weakness, yellow mucous membranes or bleeding within minutes to hours. Either way the illness can progress rapidly to death.432

What to do right after possible contact

Move the dog away from the water and do not let it drink more. If it went in, run clean tap water over the coat and skin for at least 5 minutes, until the water running off is clear, and prevent licking: rinsing is meant to stop the dog swallowing toxins while grooming.

Then contact a veterinarian or emergency clinic immediately, even if the dog seems well. There is no specific antidote: treatment is intensive supportive care, and the most useful information for the team is where and when contact happened. If you can, note the location and take a photo of the water.21

How to prevent exposure

Before a trip to a lake, check local advisories. Near lakes and ponds keep your dog on a leash and do not let it swim or drink where blooms have been seen or during the warm, dry spells that favour them. Carry drinking water and a bowl, remove standing water around your home and report a possible bloom to your local health or environmental authorities.21