Significant fish kills in both the Ballina and Tweed areas have come about because of the recent flooding say council reps.
In the Tweed, a ‘blackwater’ event has killed thousands of juvenile fish and prawns in the Cudgera Creek Estuary at Hastings Point.
Tweed Council has confirmed that the cause of the fish kill is a total absence of dissolved oxygen within the waters of the creek.
Waterways Program Leader Tom Alletson says this is called a blackwater event. ‘The floodplain of Cudgera Creek, like that of Cudgen (Kingscliff) and Mooball (Pottsville) creeks, has been inundated by stagnant floodwaters for more than a week,’ said Mr Alletson. ‘Beneath this shallow water, thousands of tonnes of vegetation is decaying and consuming oxygen.
Mr Alletson says as the de-oxygenated water drains off the floodplain and into the creeks, it displaces all the good quality water and fish cannot breathe.
The weekend’s hot weather has exacerbated the loss of oxygen.
The fish kill in Cudgera Creek has been extensive, resulting in the loss of many thousands of fish of different species, in particular smaller animals.
‘It’s possible that larger fish have moved out of the creek into the ocean, but we have lost vast numbers of small prawns and the juvenile stages of many important species.
North Creek Ballina
Down at North Creek in Ballina, Cr Keith Williams says there are dead fish everywhere along the high tide line. ‘We can expect more elsewhere in the Richmond,’ he said.
Cr Williams says that in the 2008 fish kill, North Creek was habitable and provided safe haven for many fish. ‘It doesn’t look like that’s going to happen this time.’
Cr Williams says that undoubtedly the flooding rains after a long dry period have pushed a lot of organic matter into the creeks and rivers. This provides the food for algal blooms that strip oxygen from the water and leads to the mass suffocation of fish.
‘In this instance, it looks like this is from the release of Monosulfidic Black Ooze (MBO) from the rural drainage network in the acid sulfate soil areas to the North (behind Lennox Head).
‘Also the Ballina Nature Reserve has been a major source of poor quality water for many years with very little action by NPWS to remediate old drainage infrastructure in the reserve to allow greater saltwater flushing of the estuarine swamp habitat.’
On the Tweed, Tom Alletson says it’s another big loss for our environment.
‘There are still large areas of the floodplain inundated, in the catchments of Cudgera, Mooball and Cudgen creeks.
‘While it is likely that we have seen the worst of it at Hastings Point, there is a significant risk that a similar event will play out at Kingscliff and Pottsville.
Council will work with NSW Department of Fisheries to investigate and document this event and its cause.