WWW.SEALINE.CO.ZA MORTAL STRUGGLE: dead and dying carp during a big die-off in one of the pans at the Strandfontein wastewater treatment works, which is a popular fishing spot. The image was posted on-line by a freshwater angler

John Yeld

Environment & Science Writer

HUNDREDS of big carp have died in one of the major pans at Strandfontein wastewater treatment works adjoining Zeekoevlei, temporarily ruining one of the Peninsula’s premier freshwater fishing spots.

The pans are also a major birding area, and when the incident occurred last weekend anglers and birders were ordered to leave by security staff.

This prompted speculation there had been a sewage or chemical spill into the pan, but the City of Cape Town said the fish die-off was caused by natural oxygen depletion.

“Flippen heartsore!” commented one angler on the online forum of Sealine (SA African Angling and Boating Community) that was headed “J-Dam terrible news”.

Another posted: “Hundreds of dying fish! All from 2-15kg. A couple of guys tried to ‘help’ the fish back into the water, but they just beached themselves again. There were also two guys picking up bucket loads of the fish and driving off with them. One of the most tragic things I have ever seen!”

Ossie Asmal, director of environmental resource management at the city council, confirmed that about 500 carp, “all of a larger size”, had died in the pan, but said it had not been caused by any toxic or sewage spill.

“This was due to an oxygen-depletion event brought about by a variety of factors such as the high nutrient levels, low summer water levels, calm conditions and stirring of sediments with inflowing water. An oxygen-depletion event is a natural occurrence that can occur in nutrient-enriched systems (that are) both natural and man-made.”

The dead fish were removed and disposed of at Vissershok landfill site after being tested to exclude poisoning as a possible cause of death, he added.

“The fish die-off has only affected a small part of the 350-hectare water pans on the site and is not expected to have any long-term effects.”

Security staff had instructed people not to fish during the die-off and clean-up operation as a precautionary measure.

Asked why it had been necessary to clear the area, Asmal said the guards had “erred on the safe side”.

Cape Bird Club committee member for conservation Dr Dave Whitelaw said his preliminary enquiries suggested that the die-off had been because of low oxygen levels as a result of high temperatures and eutrophication (excessive nutrients stimulating excessive plant growth).

An angler commented online: “Not good to see but with the system being what it is there is always that risk. Fish kills just like this in 1998 decimated the 15-20kg fish that were in the dams and there was no fishing for months after that. I hope they get the dam flushed out in a hurry before too many more fish die.”

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