Blue-green algae is now posing a health risk at several lagoons in the Maitland area.
Recent tests have seen high alerts issued for Walka Water Works and Telarah Lagoon, while there’s medium-level concern about Rathulba Lagoon.
The algae can cause nausea and skin irritation.
It’s believed recent warm temperatures and nutrients in the water have provided an ideal environment for the bloom.
Maitland Council says it’s monitoring the situation.