Once, much of the Nile delta was composed of marshes and brackish lagoons, protected from the sea by sand bars. Today the lagoons have been reduced by drainage, and are increasingly polluted by sewage and pesticides. Lake Maryut, once a haven for wildlife depicted in Lawrence Durrell's Alexandria Quartet, is now a cesspit for the metropolis of Alexandria. It is a very rare rare when Nile waters are allowed to pass naturally through the lagoons into the sea. Fish catches there dropped by 85% in the 1970s. The sewers of Cairo, a city of 10 million people, empty into the equally foetid Manzala lagoon. The four surviving lagoons supply 100,000 tonnes of fish annually (two-thirds of Egypt's catch) and employ 100,000 people. But these may soon disappear with the sea erosion of the protective sandbars which are deprived of silt since the Aswan dam was built in 1964.