A bull terrier died after drinking water at the margin of Zeekoevlei near Cape Town. At the time, Zeekoevlei, a hypertrophic coastal lake, contained a bloom of the cyanobacteria Nodularia spumigena and Microcystis aeruginosa. The circumstances of the incident, clinical signs of poisoning and histopathology, which mainly revealed extensive liver damage, were consistent with cyanobacterial poisoning. The cyanobacterial bloom material contained 3.47 micrograms mg-1 dry weight of the pentapeptide hepatotoxin nodularin. It is inferred that the dog died of cyanobacterial hepatotoxicosis due to the ingestion of nodularin.