The Blackstaff River is a watercourse in County Antrim, Northern Ireland. It rises on the eastern slope of the Black Mountain before flowing down into the Bog Meadows and passing under the city of Belfast, where it enters the River Lagan. Much of its course has been culverted and built upon since the 19th century, making it largely invisible today. Its tributaries include the Forth or Clowney River, which meets it beneath the Broadway Roundabout in West Belfast.