A few miles off the coast of Durban a female humpback whale and its calf – the last of thousands that migrated along South Africa’s east coast from May to December – splash their fins playfully on the surface of the Indian Ocean.

Out in the deep, they are unperturbed by a murky brown sheen sitting on the surface of the South African city’s harbour, where brilliantly white yachts worth millions of rand float in water contaminated with human excrement.

“We all call it Shit Creek,” said Brad Groddler, 50, a boat captain who takes tourists out for whale-watching and fishing trips.

Ever since deadly floods in April last year damaged an already ailing sewage and water system, millions of litres of untreated sewage have spilled into the beaches, rivers, harbours and ocean in and around Durban.

Between April and December many of the city’s beaches – which usually draw hundreds of thousands of tourists for the southern hemisphere’s summer – were closed after critical levels of E coli, a bacteria that can cause diarrhoea, vomiting and fever, were found in the water.

Nine months after the floods, environmental scientists say contamination is still a big problem.

“We’ve had mass fish kills on the Umgeni River system [and in] Isipingo and Umhlanga,” said Siraj Paruk, an environmental specialist, “mainly due to sewer inflows into these systems which cause the oxygen…