Lake Simcoe is southern Ontario's largest body of water excluding the Great Lakes. It serves as an important recreational resource for cottagers, anglers, campers and boaters. The population of the lake's basin was approximately 190,000 people in 1985. During the summer, there is an influx of 40,000 to 50,000 cottagers who occupy the 12,000 cottages surrounding the lake. Seventy percent of these cottagers rent or own boats and 35 marinas provide a moorage for the larger boats and yachts that can then access the Trent-Severn Canal System waterway which connects Lake Simcoe to Georgian Bay (via the Talbot River), Lake Huron, Lake Ontario and the Rideau Canal System which allows boats to reach the nation's capital and from there, the Ottawa River and the St. Lawrence.

Lake Simcoe's shoreline is composed of 55% cobble, 35% sand and 10% organic muck. The lake is located within the eastern portion of the Simcoe Lowlands where well-drained till soils predominate. Along the northern and western shores of the lake, the lowland consists of a narrow bouldery terrace confined by a low bluff. The southern and eastern shores are characterized by poorly drained sandy loams and large organic deposits located along the major river courses.

The lake's basin is drained by 35 tributary inflows with 5 major rivers draining approximately 60% of the watershed area. Annual mean discharges for the major river systems range from 2 to 4 m3 s-1. Peak flows range from 20 to 60 m3 s-1 and usually occur during the spring melt period.

The 1980 survey of Ontario sport anglers indicated that Lake Simcoe received more fishing effort than any other Ontario inland lake. During the winters of 1980-1983, 400,000 to 500,000 angler-hours were spent on the lake during each winter and 2,000 to 3,000 ice fishing huts were rented during each year. Lake Simcoe's proximity to major urban centres in the Oshawa-Toronto-Hamilton corridor is primarily responsible for the intense sport fishery that exists on the lake, which is located about 50 km from Toronto and is within an hour's drive for over half the population of Ontario.

Water quality in the lake has been affected by an excessive supply of phosphorus which has stimulated an over-growth of aquatic weeds and algae in certain parts of the lake. This results in critically low dissolved oxygen levels in deep portions of the lake which in turn has been linked to a decline in whitefish and lake trout populations within the lake. Beginning in 1975, lake shore municipalities. Ontario ministries and conservation authorities responsible for Lake Simcoe began working together to study the lake and in 1979 they published the Lake Simcoe-Couchiching Basin Environmental Strategy which evaluated measures designed to reduce phosphorus inputs to the lake. This strategy also established baselines for physical, chemical and biological data, some of which are described below. Considerable reductions in point source phosphorus loading have been achieved in recent years. Present-day inputs (1989) may be near acceptable levels (2, 3, 4, 5, 7, 8).