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

Scientists have proved that slugs found on an Auckland beach are toxic but have not established what they have eaten to make them poisonous.

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.