This hydrographic slope originates from Rodayer Lake (length: 67 kilometres (42 mi); altitude: 250 metres (820 ft)), located at 10.4 kilometres (6.5 mi) north of the Nottaway River, at 14 kilometres (8.7 mi) north of Desorsons Lake (elevation: 254 metres (833 ft)) and west of Utamikaneu Lake (surrounded by marsh, altitude: 261 metres (856 ft)).

From Lepallier Lake, the Lepallier River flows over 39.3 kilometres (24.4 mi), first to the northwest, then to the north, collecting the waters of the Louvart River (coming from the South-East) and crossing several marsh areas.

The Lepallier River is accessible from the Rodayer Lake campground, near the "James Bay Road".

The Lepallier River is accessible from the Rodayer Lake Campground, near the "James Bay Road".

The toponym "Lepallier River" was formalized on December 5, 1968, at the Commission de toponymie du Québec.