Cape Town -

Further warning of a so-called red tide in the Knysna estuary on the Cape south coast was issued by SA National Parks on Monday.

“Authorities - including SANParks, Knysna Municipality and the Knysna Basin Project - are cautioning against the collection of shellfish from the Knysna estuary until further notice,” it said in a statement.

A red tide is the common name for an algal bloom involving large concentrations of red or brown coloured micro-organisms. These can become concentrated in filter feeders such as mussels and oysters, making them poisonous to humans.

Other types of shellfish, including abalone, are also affected.