The river is 15.3 square miles in length.[1] Its headwater is heavily urbanized watershed; in addition to Bridgeport and Fairfield, it also runs through Trumbull.[1] Rooster River extends southward into Long Island Sound by way of the Ash Creek Estuary.[1] The source of the river is Lake Forest in Bridgeport, Horse Tavern Brook in Trumbull, and London's Brook from the Fairchild Wheeler golf course. For a short distance upstream from the junction with London's Brook (which is adjacent to Unquowa School) into Bridgeport both 'Horse Tavern Brook' and 'Rooster River' have been interchangeably used.[2]