The warning was issued after a spike in reports of toxic blue green algae in several locations across the UK.
Known as cyanobacteria, the algae may contain dangerous toxins which can be fatal to pets and livestock if ingested – even in small quantities.
Blue green algae blooms may appear as green or greenish-brown scum on the surface of water.
Dogs can swallow it by drinking water from an affected lake, river or pond. Symptoms can appear within a few minutes or hours, depending on the toxin, and commonly include vomiting, diarrhoea, drooling, disorientation, trouble breathing, seizures and blood in faeces.
Daniella Dos Santos, BVA president, said: “There is currently no known antidote for the toxins, so prompt veterinary treatment is the only way to tackle their effects and ensure a good chance of recovery.
“If you suspect your dog has been exposed, seek emergency veterinary treatment as soon as possible.”