Thousands of dead fish have washed up on the shores of the Richmond River in Ballina, northern New South Wales, following flooding caused by ex-Tropical Cyclone Alfred, according to conservation group OzFish.

The organization has reported numerous accounts from the public, including photographs and messages of the fish kill, showing fish struggling for air or washing up dead.

Additionally, reports of mud crabs and eels leaving the water due to the conditions have also been received.

A “blackwater” event, where organic material washed into waterways leads to oxygen depletion, is believed to be the cause of the fish kill. The decomposing organic material can suffocate fish and other aquatic life.

OzFish CEO, Cassie Price, stated that photographs have shown dead flathead, bream, whiting, prawns, and other marine life. Volunteers have tested the water quality along the Richmond River, with the results indicating a severe shortage of oxygen, with levels being less than one-tenth of the required 5mg of oxygen per litre.

Price said that the dissolved oxygen levels in the Richmond River are currently almost non-existent, at 0.4mg per litre. She emphasized that fish experience distress when oxygen levels drop below 4mg/L and die at 2mg/L.

OzFish has called for urgent action to prevent further fish kills, including the restoration of swamplands along the Richmond River catchment. These swamplands can filter out blackwater, thus reducing its severity and protecting aquatic life.

Source: https://www.theguardian.com/australia-news/2025/mar/16/thousands-of-fish-die-in-cyclone-hit-northern-rivers-amid-reports-of-eels-and-crabs-fleeing-blackwater