Tetrodotoxin found in the dead dogs' vomit and in a sea slug sample taken from Narrow Neck Beach.

Researchers believe they may be dealing with two or even three unrelated causes of illness in the Hauraki Gulf.

Health authorities have issued an alert for all eastern Auckland and Hauraki Gulf beaches after two dogs died and others fell sick.

Dog owners are being warned to keep away from North Shore beaches after the deaths of two dogs.