A recent major fish kill in northeast NSW at Lake Cudgera resulted in over 7 thousand fish being killed in the lake.

The results of tests carried out on the reasons for this kill indicated that it was most likely caused by acid sulfate run off from a nearby housing development project.

This region of the Tweed valley has long been known as a major acid sulfate area and it was recognised many years ago that the mysterious fish kills in the Tweed river, after a dry period followed by heavy rain, was the result of acid sulfate run off.

The Richmond, and to a lesser degree, the Clarence River also suffers from acid sulfate problems.

The nearby coastal town of Evans Head has a major problem with acid sulfate soils. Recently a major development here was halted at great expense after it was proven that the site was running sulfuric acid in huge quantities from a major drain which ran through the development. An Environmental Court Judge decided after expert advice that the problem of acid sulfate soils on the development could not be managed with enough certainty to warrant the completion of the project. He ordered that the project be stopped, restored and revegetated, to minimise the damage already caused.

At the writing of this report there has been a worrying development in Evans Head where the domestic drinking water has been found to be contaminated by unacceptable levels of copper and other heavy metals. It appears that the high acid content in the water supply is leaching the copper from the copper pipes carrying domestic water to homes in the town. To date the local council is extremely worried, as it does not yet have a solution to the problem. At this stage, there appears to be no viable solution in sight.

The reaches of the Richmond River near Ballina also suffer from fish kills and red spot disease on a regular basis due to the leaching of acid sulfate from major drainage works further up river.

 In the case of the Tweed river, the major cause of fish kills in the area seems to be acid sulfate run off, from major drainage works which have been completed for over forty years, through the cane fields. During those years fish kills have occurred when conditions are right; mainly a period of dry weather and then reasonable heavy rains following.

Unfortunately there seems that, at this stage, there is little which can be done to stop the fish carnage which is occurring with monotonous frequency.

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