Cape Town - The City of Cape Town and other government departments are currently investigating what killed the large number of fish which washed ashore at Milnerton Lagoon. The dead mullets (commonly known as harders) started washing up on the shoreline on 15 March. "The exact cause is being investigated, but may be difficult to determine," the City's Wilfred Solomons-Johannes said in a statement."It is suspected, however, that the fish deaths could be attributed to high nutrient levels, high water temperatures and low oxygen levels." Summer low water levels could have added to the low available oxygen, Solomons-Johannes added. "At this stage there is no evidence of any toxic spill." He said samples of fish tissue were being analysed by the department of agriculture, fisheries and forestry. Meanwhile, members of the public are advised not to collect or eat the dead fish, the statement said. In addition, recreational users of the vlei and local residents are urged to avoid swimming and other water-based recreational activities such as canoeing downstream of the Otto du Plessis Drive bridge. To date, approximately 10 tons of fish have been removed and taken to the Visserhok landfill site and a further 5 tons are expected to be cleared away.Milnerton Lagoon, an important estuarine habitat on the West Coast, is part of Table Bay Nature Reserve, one of the 16 City owned and managed nature reserves.