Lake Mégiscane is located in forest in Abitibi, between Lebel-sur-Quévillon and the Gouin Reservoir. The main lakes surrounding are:

• north, Cherrier Lake,
• to the east, the lakes Canusio, Ouiscatis and Dumont,
• in the West, Kamiskonamebanikâk, Kâmâkociwak, Maricourt and Berthelot lakes.

The shape of Lake Mégiscane is very complex. This lake is made in length (from south-west to north-east), with three important enlargements:

• the southern part of the lake is 8.5 kilometres (5.3 mi) (including the strait connecting it to the central part) and its maximum width is 1 kilometre (0.62 mi). The Bay of Wolves is located on the west shore;
• the central part has a length of 8.5 kilometres (5.3 mi) by 8.5 kilometres (5.3 mi) of maximum width. It has a large island of 32 kilometres (20 mi) with 18 kilometres (11 mi) at its center;
• the northern part has a length of 9.0 kilometres (5.6 mi), with a maximum width of 6 kilometres (3.7 mi). Lake Arlette flows into the northern part.

Lake Mégiscane flows through the north of its central part, into the river of the same name.

• James Bay
• Nottaway River, a watercourse
• Matagami Lake, a water body
• Bell River, a watercourse
• Mégiscane River, a watercourse
• Abitibi-Témiscamingue
• Senneterre (parish)