Toronto Harbour, Natural harbor in Toronto, Canada.

Toronto Harbour is a natural bay on the north shore of Lake Ontario, sheltered by the Toronto Islands. It is split into the Inner Harbour, entered through the Western Gap or the Eastern Gap, and the Outer Harbour, built in the 1950s and 1960s behind the Outer Harbour East Headland. The Don River reaches the Inner Harbour through the Keating Channel.

The harbour's north shore was originally low sandy bluffs just south of today's Front Street, with the bay mouth pointing west and a sandy peninsula forming its southern limit. Sand eroded from the Scarborough Bluffs, about 10 km east, was carried west by lake currents to build that peninsula. The town of York, founded in 1793 in a ten-block rectangle bounded by Front, Berkeley, Duke (now Adelaide) and George Streets, built a government wharf to handle ships' cargoes. The Eastern Gap opened when storms broke the spit between 1852 and 1858, and the Harbour Trust later made it permanent.

The harbour's name is recalled in the Seneca legend of Gaasyendietha, a lake-monster figure said to appear in Lake Ontario and sometimes in the bay. On the water, the Jack Layton Ferry Terminal at the foot of Bay Street sends ferries to the Toronto Islands, while pleasure and party cruise boats dock west of York Street.

The Inner Harbour is entered through the Western Gap, a 120-metre channel over 31 metres deep, or the roughly 200-metre Eastern Gap used by most freighters. Ferries to the Toronto Islands leave from the Jack Layton Ferry Terminal at the foot of Bay Street, and Billy Bishop airport is reached by ferry and tunnel.

The Redpath Sugar Refinery on the north shore is the last port-related industrial use there; most surrounding land became Harbourfront parks and cultural facilities. Cargo ships still deliver raw sugar to it. The harbour also holds Gaasyendietha, a Seneca legend of a lake monster said to appear in Lake Ontario and sometimes in the bay.