The islands were a peninsula extending from the mainland until a fierce storm in 1858 washed away a noticeable portion of the connecting landmass. The largest, outermost island, commonly called Centre Island, is crescent-shaped and forms the shoreline of both the Eastern and Western Channels. Algonquin and Olympia are two of the other major islands. Ward's Island is actually the eastern end of Centre Island.
Geologically, the islands are composed of alluvial deposits from the erosion of the Scarborough bluffs.
The human use of the islands has changed over the years. Industrial envelopment and landfill brought the shoreline approximately 900 feet in to the harbour from the natural shoreline of Front Street. Presently (2003) a small residential community is located on Algonquin and Ward's Islands (see ). The central area hosts a children's amusement park, Far Enough Farm, three yacht clubs, swimming beaches, including a nude beach, picnic grounds, and a boardwalk. The island also contains the Island Public and Natural Science School, rental artist studios and housing (Gibraltar Point Centre for the Arts), a dragonboat regatta grandstand, and a water filtration plant. Three ferry routes connect different parts of the islands to docks at the foot of Bay Street.
Toronto City Centre Airport (YTZ), formerly the Toronto Island Airport and still commonly known as the Island Airport, is located at the far west of the Islands and reached by a separate, much smaller ferry from the foot of Bathurst Street. It serves recreational aviation, medical emergency, regional business flights, and flight schools. There is no public access between the airport and the park. In 2002 Toronto's city council approved the controversial construction of a bridge to replace the airport ferry, but this is strongly opposed by David Miller, who won the 2003 Toronto election for mayor.
Private cars are not permitted on any of the Islands. Service vehicles and some delivery vehicles are permitted. Recreational bicyclists are accommodated on the ferries, and bicycles and quadricycles can be rented on the islands. The Marine Units of the Toronto Fire and Police Departments patrol the waters.
For a comprehensive and well-illustrated history of the Island, read Sally Gibson's "More Than an Island" Toronto:Irwin, 1984