It is located along the Cowichan Valley in the Cowichan Valley Regional District, with its eastern shore about 28 km (17 mi) west of Duncan, British Columbia.

Cowichan Lake is about 30 km (19 mi) in length, running mostly from west to east, and is about 4 km (2.5 mi) wide at its widest point.

The Cowichan Valley was once a thriving lumber centre in British Columbia.

In the past, two major railroads had spur lines to and around parts of the lake.

With the change in the logging industry, these rail lines have now been abandoned by the railroads and are now part of a major public trail system which leads eastward toward the lower end of the Cowichan Valley.