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Byron Shire
October 20, 2021

Flooding the cause of fish kills in Ballina and Tweed

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Many thousands of juvenile fish and prawns have been killed in Cudgera Creek. Photo supplied.

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.

A fish from North Creek in Ballina. Photo supplied.

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.’

Dead fish in North Creek in Ballina. Photo supplied.

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.

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  1. Am I alone in marvelling at the complete absence of any mention of the horrific levels of pesticides,fungicides , herbicides and poisonous fertilisers flushed out of local plantations…. and the well documented toxic loads from suburbs and industrial areas ? While the “Monosulfidic Black Ooze (MBO) from the rural drainage network in the acid sulfate soil areas” is mentioned ,no explanation that these areas have been created by drainage systems negligently draining acid-sulphate wetlands for private profit, and now constantly dumping thousands of tons of sulphuric acid into local estuaries.
    But hey ! it must be that terrible fresh water ,organic matter, Nature Reserves and that pesky NPWS.
    You Know it’s True. G”)

  2. Why is it so hard to believe that the decomposition of organic matter via microbes is responsible?
    It’s basic biology and chemistry. Anyone with a fish-pond has seen similar decay-associated de-oxygenation.
    There’s enough evidence of the consequences of farms and fertilizers for people to digest without further muddying of the waters with such false attribution of blame in one of the rare instances that farming practices are not the driving cause of a particular ecological degradation.

    Wild accusations without evidence will only turn more people away from respecting the science and institutions urging us to act on environmental issues.

  3. Not surprising where you see such a lack of vegetation diversity along many creeks. The government could be helping landowners change this.

  4. Wild Bird Life is affected by de-oxygenated water.

    For example the Botulism Toxin may enter a birds central nervous system causing paralysis in wings, legs, and neck.

    Birds may drown because they can not lift their heads’ up out of the water.

    Call a Local Wildlife Group for advice – or – to report a sick or injured seabird / water bird.

  5. What about ALL of the toxic fire retardants this heavy rainfall has washed OFF the land, OUT of the bushfire zones, and INTO the waterways, creeks, rivers, dams, and sea!?!?


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