Cold weather kills Bony Bream at Split Rock Dam

The grim discovery was made on Tuesday afternoon, with the native Bony Bream either belly up in the water or washed ashore.

NSW DPI’s Murray Darling Program Leader Cam Lay said while it looked dramatic, it was not an uncommon phenomenon.

“We believe the rapid change in temperature suppresses their immune system and they die of a parasitic infection or some other type of bacteria,” Mr Lay said.

“We think that’s the mechanism that causes it –  we’re not 100 per cent sure, but we do know there is a direct link to cold water temperatures.

“We see it occasionally at this time of the year on cold and still nights. It often effects dams or other large bodies of water with little movement, which can rapidly lose heat overnight.”

The early morning temperature at Split Rock Dam has been dropping below -2 degrees this week.

Mr Lay said it was not an event to be overly concerned about, give the size of Bony Bream population.

“Often the wind blows all the fish to one point, so it looks quite dramatic, but it only represents a small proportion of the population,” he said.

“They are an extraordinary abundant fish, and one of the most wide-spread native freshwater fish we have.

“Ironically, they can survive in a wide temperature range, so they’re found right across the country, but they are susceptible to rapid reductions in temperature.”

Mr Lay said the fish were also very sustainable to cold water population.

“Dams and weirs often release water in to the environment at very cold temperature, much colder than the environment it’s entering,” he said.

“The fish themselves are widely distributed, but their populations are reduced directly downstream of dams, where cold water pollution is a problem.”

A spokesperson from WaterNSW, who look after the Split Rock Dam, also pointed to the cold weather.

“A number of native Bony Bream have washed up on the dam foreshore, not an uncommon occurrence at regional dams during winter,” the WaterNSW spokesperson said.

It is expected authorities will let Mother Nature take care of the clean up job.