Trout Lake has a total surface area of about 1700 hectares, split about 80% / 20% between Trout Lake proper and Four Mile Bay, respectively. The perimeter of the lake is about 60 kilometres long of which 75% is within the boundaries of the City of North Bay and 25% within the boundaries of the Township of East Ferris. The Lake has a maximum depth of 68 metres and an average depth of 17 metres. Its average pH is slightly above 7, which makes it slightly alkaline. Thus Trout Lake has not suffered acid rain effects as it has a natural buffering capacity.

Trout Lake is the headwaters for the Mattawa river which drains into the Ottawa river. The junction of these two rivers is in the town of Mattawa. A geological fault line heads east along the Mattawa river, and periodically small earthquakes are felt in the Trout Lake watershed, most originating from this fault line. Important granite cliffs line the Mattawa. Ten thousand years ago, the Great Lakes emptied through the Mattawa, into the Ottawa and then into the St-Lawrence. When the glaciers melted the land rebounded and eventually the Great Lakes starting draining south rather than northeast. For thousands of years, the water levels of the Great Lakes were controlled by Trout Lake drainage area ! This rebound eventually caused lake Nipissing to separate from Trout Lake. Today a 9 km land bridge separates these two lakes, with Trout Lake flowing east and lake Nipissing flowing south to Georgian Bay, Lake Huron and beyond, eventually reaching the St-Lawrence and the Atlantic Ocean.

One of the convenient ways in which scientists classify lakes is by their "trophic status". Trout Lake is a good example of an oligotrophic lake. This implies a cold, clean, deep lake with low nutrient levels and consequently low productivity. These kind of lakes usually support a cold water fishery such as lake trout, and in the case of Trout Lake, ouananiche.

The Watershed

The Trout Lake watershed includes all lands that drain into Trout Lake. Its surface area is approximately 11 000 hectares. The long axis of Trout Lake runs east-west, and the topography of the northern portion of the watershed is very different from that of the southern portion of the watershed.

The northern portion of the watershed is characterized by steep slopes. Several fast-flowing streams such as Four Mile Creek cascade down the escarpment into Trout Lake. The southern portion of the watershed is flatter, with sandy soils, rolling hills and important wetlands. The southern portion of the watershed harbours heronries (in the wetlands) and a host of other wildlife such as deer, moose, otter etc.