Deadly algae contaminates major NSW waterway

Rare toxic algae that can prove fatal to humans has been detected in a South Coast river just weeks after a catastrophic silo collapse caused hundreds of tonnes of wheat spill into the water.

Water NSW issued an alert after the algae Alexandrium minutum were picked up in the Shoalhaven River at Nowra, about a kilometre upstream from the Manildra starch factory, where two wheat silos collapsed last month.

The algae can cause paralytic poisoning in humans if they eat contaminated shellfish, which can prove fatal in extreme cases. Mild cases can trigger numbness and tingling, as well as headaches, vomiting and diarrhoea.

Oyster farms about 15 kilometres downstream from the factory were closed last Friday after the algae were detected, but the Department of Primary Industry reopened them on Thursday after testing found the harvest area, and the oysters, were safe.

The Shoalhaven is a key oyster region in NSW, with farms at Shoalhaven Heads and Greenwell Point. The department said testing would continue weekly as the industry heads into its busiest time of the year.

But the public has been told to avoid eating wild shellfish they might collect themselves from the river near the Nowra Bridge, and to avoid the water at the recreational spot, which is popular with water skiers. Fin fish should be cleaned thoroughly.

The algae were detected during testing after the collapse of two 30-metre-high silos at Manildra on October 17. The silos each contained 1000 tonnes of wheat when they collapsed about 10pm, with the contents of one ending up in the river. A third silo was also destroyed.

SafeWork and the Environment Protection Authority are investigating the collapse at the factory, which makes wheat starch, gluten and ethanol.