The incident took place when two girls - Sadhiha (13) and Saleaha (9) had gone to wash clothes at the K C canal, Alampur police station sub inspector Parvathalu said.
The girls slipped into the canal. Saleaha's body has been found, while efforts are on to trace Sadhiha, he said.
A case under relevant sections of IPC has been registered and investigations are underway, police said.