Lac des Mille Lacs has an area of 245.1 square kilometres (94.6 sq mi) and a drainage basin of 1,774.55 square kilometres (685.16 sq mi).

The outflow to the Seine River is controlled by the Lac des Mille Lacs Dam, owned by the Ontario Ministry of Natural Resources (OMNR) and operated by the Valerie Falls Limited Partnership (Brookfield Renewable Power).

[1] The first dam at the site was built of stone by Simon James Dawson of the Department of Public Works Canada in 1873 to improve water flow for navigation to the vicinity of the Red River of the North far downstream.

[2] This dam was replaced in 1926 by a timber dam to regulate water flow used for hydroelectric power production downstream on the Seine River and Rainy River.

[3] The First Nation, which is currently dispersed throughout Northwestern Ontario rather than living on its traditional lands, has a land claim pending negotiation with the federal and provincial governments.