Encompassing 908 km2 in total, the Humber River watershed is the largest in the Toronto region. The 126-kilometre long Humber River has its headwaters in the ancient rock of the NIAGARA ESCARPMENT and the glacial hills of the Oak Ridges Moraine. It flows placidly through a rich mosaic of Carolinian forests and meadows, past farms and abandoned mills, before meandering through the largest urban area in Canada, TORONTO. At its mouth, on Lake ONTARIO, are the HUMBER MARSHES. Lieutenant-Governor John SIMCOE named the Humber after a river in England.

The Humber is in the backyard of nearly six million people, a river that flows through the most densely populated area of Canada but still retains many of its natural values. Today, approximately 45% of the watershed is urban or urbanizing, and 55% of the watershed is rural. The river is being protected and restored with the help of many individuals, groups and agencies who share a common vision of an ecologically healthy river oasis in an increasingly urbanized area. The vision is slowly being fulfilled, as brook trout thrive in the river's headwaters and its wetlands ring with the choruses of birds and frogs. A system of trails along its course maintains the spirit of the Toronto Carrying Place Trail, the historic overland route from Lake Ontario to the interior followed by Aboriginal peoples and then European explorers and settlers. In 1999 the river was designated as a CANADIAN HERITAGE RIVER.