 One of them is the Dandora Waste Stabilisation Pond System which treats the industrial and domestic sewage from the city of Nairobi and is the largest pond system in Africa.Mixing industrial effluent and domestic sewage in mixed sewer system, however, often causes poor performance in Kenyan pond treatment systems.The Citizen Report Card moreover indicates that septic tanks are often used for the disposal of wastewater from flush toilets in Mombasa.