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Rietvlei Fish Mortalities - December 2006
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Christmas Day brought an unpleasant surprise to residents of Table View when thousands of dead fish washed up on the shores of Rietvlei. From 25 to 28 December 2006 an estimated 80 tons of dead fish were removed from Rietvlei. The vlei was closed to recreational use and only re-opened on 10 January 2007.

Routine water sampling in the North Vlei on 19 December 2006 showed normal results for that waterbody. However, during the hot, windless days leading up to Christmas the water temperature rose by over 8 degrees Celsius and dissolved oxygen levels dropped. This is assumed to have affected the largely estuarine fish species harders/southern mullet, springer/flatheaded mullet and estuarine round herring, causing an extensive die-off.

The deaths of such large quantities of fish led to a massive clean-up operation being undertaken by staff of the City of Cape Town and volunteers from the Milnerton Aquatic Club, Friends of Rietvlei and the general public. This clean-up was undertaken as a matter of urgency to prevent a health nuisance as well as to prevent the water body from being further contaminated by rotting fish. It is estimated that 80 tons of dead fish was taken to the City's Vissershok landfill site.

Water samples taken on 8 January 2007 indicated results that were normal for the area. Sampling of water is essentially a "snapshot" in time. Since water quality can change very rapidly, users should always be cautious and use common sense if the water looks abnormally green, is odorous or if dead fish/other animals are observed. Unusual fish behaviour such as erratic swimming/gasping at the surface could signify the onset of low oxygen conditions which the City should be made aware of. Regular users of the area are valuable as "field eyes" and can help the City with early response to abnormal environmental conditions.


On the next pages are some pictures of the fish die-off in Rietvlei.
 
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