For the past five years Hyderabad has been trying to clean the Hussain Sagar Lake, separating the twin cities of Hyderabad and Secunderabad in Andhra Pradesh. The efforts suffered yet another blow on June 20 when the Andhra Pradesh Pollution Control Board (APPCB) denied permission to dredge the mouths of four nalas releasing waste water into the lake and to dispose it of at a nearby quarry. It said the sediments contain hazardous chemicals.