Mesplet Lake has a total length of 20.3 kilometres (12.6 mi) and a maximum width of 4.2 kilometres (2.6 mi). On the Northeast side, this lake has a marsh area. The surface of this lake is an altitude: 393 metres (1,289 ft) like other surrounding water bodies. Having a complex configuration, this lake resembles a large recumbent S whose end to the northwest is formed by the Bay of Cedars (length: 4.1 kilometres (2.5 mi)) and "Baie de la Truite" (English: Trout Bay) (length: 2.3 kilometres (1.4 mi)). The southeastern extremity has a bay (length: 3.1 kilometres (1.9 mi)) surrounded by marshes.

The mouth of Mesplet Lake is located in the center of the south shore of the lake. From there, the current crosses southwards the "Mesplet Pass" (length: 2.1 kilometres (1.3 mi)), which connects it to Cherrier Lake. This mouth of Lake Mesplet is at: North of the mouth of Cherrier Lake;

• 19.2 kilometres (11.9 mi) north-east of the confluence of the Saint-Cyr River South with the Mégiscane River;
• 24.1 kilometres (15.0 mi) north-east of the mouth of the Mégiscane Lake which is crossed by the Mégiscane River;
• 106.1 kilometres (65.9 mi) north-east of the mouth of the Mégiscane River (confluence with Parent Lake (Abitibi);
• 360.4 kilometres (223.9 mi) south-east of the mouth of the Nottaway River (confluence with Rupert Bay);
• 62.2 kilometres (38.6 mi) west of the village center of Obedjiwan;
• 95.5 kilometres (59.3 mi) east of the village center of Lebel-sur-Quévillon.

The main hydrographic slopes near Mesplet Lake are:

• north side: Loutres Lake, Macho River, Panache River, Fortier River (Panache River tributary);
• east side: Robertine Lake, Barry Lake (Saint-Cyr River South), Bailly Lake (Saint-Cyr River South), Saint-Cyr River South, Aigle River (Doda Lake), Pascagama River;
• south side: Cherrier Lake, Saint-Cyr River South, Canusio Lake, Mégiscane Lake, Mégiscane River, Kekek River;
• west side: Masères Lake, Closse River, Macho River, Wetetnagami River, Mégiscane River.

• James Bay
• Nottaway River, a watercourse
• Matagami Lake, a body of water
• Bell River, a watercourse
• Parent Lake (Abitibi), a body of water
• Mégiscane River, a watercourse
• Saint-Cyr River South, a watercourse
• Cherrier Lake, a watercourse
• Senneterre, a city
• Saint-Cyr Lake Biodiversity Reserve, a protected area
• List of lakes in Canada