Dog that swims in a reservoir with algae and collapses within minutes
5-year-old Border Collie that, in late August, swam in and drank from a reservoir with greenish scum along the shore. Within 15 minutes he shows salivation, fasciculations, rigidity and stumbling, followed by flaccid paralysis with shallow breathing and cyanosis. He has had no access to baits or garden products.
What is the most likely cause and which statement is correct?
chevron_right Show answer and explanation
A. Microcystins: acute liver failure explains the signs; N-acetylcysteine and fluids
Microcystins are hepatotoxic and cause hepatic necrosis over hours; they do not explain neuromuscular paralysis at 15 minutes. The liver should be monitored, but it is not the immediate problem.
B. Organophosphate in the water: high-dose atropine reverses the whole picture
There is no pesticide exposure, and atropine only controls muscarinic signs; it does not reverse respiratory muscle paralysis, which is nicotinic.
C. Metaldehyde: the tremors and hyperthermia respond to methocarbamol
Metaldehyde causes continuous tremors and hyperthermia, not flaccid paralysis with respiratory failure, and the dog had no access to baits.
D. Anatoxin-a: there is no antidote; ventilation, decontamination and a grave prognosis
Correct. Anatoxin-a is a cyanobacterial neurotoxin that acts as a depolarising nicotinic agonist: fasciculations, rigidity, then paralysis and death from respiratory failure within minutes to hours. Treatment is supportive (mechanical ventilation, anticonvulsants, bathing with gloves).
lightbulb Key takeaway
Cyanobacterial blooms in reservoirs and slow-flowing rivers are common in summer in Spain. Neurotoxins (anatoxins): signs within minutes; hepatotoxins (microcystins): liver failure within hours. Inform public health and other owners in the area.
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Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.