Government warns of fish deaths as flood waters recede

THE health of northern NSW rivers is likely to drop significantly in coming days as flood waters recede leading to possible large-scale fish deaths, the state government has warned.

The Department of Primary Industries has issued a warning that vegetation covered by flood waters for long periods can start to rot resulting in oxygen levels in the water to drop.

DPI senior fisheries conservation manager Marcus Riches said that in coming days fish deaths were to be expected as a result.

"This 'dead or black water' then flows back into the river via the flood plain drainage network," Mr Riches said.

"Warmer water temperatures also exacerbate the situation, speeding up decomposition processes."

He said his department had been informed that decreasing dissolved oxygen levels had already been reported in some rivers.

"This is concerning as water covering major coastal floodplains have yet to fully drain into the main river systems and warm, shallow flood waters low in oxygen are yet to drain back into the river," he said.

"We are expecting the trend of decreasing oxygen levels will continue over the coming days, resulting fish gasping at the surface, or fish deaths.

"The extent and scale of fish deaths is very difficult to determine as fish can sometimes move ahead of this poor water, while at other times they are not able to get away and this can result in significant fish kills."

The department would like to hear from anyone that has observed fish kills or seen fish gasping at the surface on the Fishers Watch phoneline:1800 043 536.