The Humber collects from about 750 creeks and tributaries in a fan-shaped area north of Toronto that encompasses portions of Dufferin County, the Regional Municipality of Peel, Simcoe County, and the Regional Municipality of York. The main branch runs for about from the Niagara Escarpment in the northwest, while another major branch, known as the East Humber River, starts at Lake St. George in the Oak Ridges Moraine near Aurora to the northeast. They join north of Toronto and then flow in a generally southeasterly direction into Lake Ontario at what was once the far western portions of the city. The river mouth is flanked by Sir Casimir Gzowski Park and Humber Bay Park East.