[4] Its area is 2,940 hectares (7,300 acres) and its shoreline is 210 kilometres (130 mi) long.

[1] The lake is located primarily in the municipalities of Sables-Spanish Rivers, Baldwin and Nairn and Hyman, although its easternmost end enters the city limits of Greater Sudbury near High Falls.

It is formed by the 353.57 metres (1,160.0 ft) long and 44.50 metres (146.0 ft) high Big Eddy Dam, built in 1920, and serves as the reservoir for several hydroelectric power stations downstream.

[5][6] The lake was named after John Lyons Agnew, who became president and general manager of INCO in 1921.

[7] Fish species found in Agnew Lake include:[2] Northern pike, smallmouth bass, and walleye have consumption advisories due to mercury contamination.