The South Thompson River flows past the City of Kamloops on its way to join the ocean at the Coast and we know that the river’s waters come from Shuswap Lake (through Little River and Little Shuswap Lake), but the entire watershed area of Shuswap Lake covers 1,552,558 hectares (5993 square miles) of the province.   Generally speaking the river is the result of meltwaters of snow and rain that falls on the western slopes of the Monashee Mountain Range and regional higher areas of the Interior Plateau.

Several rivers drain the Monashees from the east/southeast:

• Shuswap River (through Sugar Lake, then Mabel Lake) – flows south, then east, then north, then west, then north for 195 km, emptying into Mara Lake
• Eagle River – flows west for 75 km, flowing into Shuswap Lake at Sicamous

From the north, three main rivers draining the northern Monashees and the Adams Plateau:

• Seymour River – flows for 71 km before draining into the eastern end of the Seymour Arm
• Adams River – flows for 131 km (through Adams Lake) to the main arm of Shuswap Creek
• Anstey River – flows south for 31 km, emptying into the Anstey Arm

From the south one major rivers drains a region of the Interior Plateau into the lake:

• Salmon River flows northeast, then east, then south for 146 km into the Salmon Arm

Many creeks also contribute to the volume of water in Shuswap Lake and the South Thompson River, including Chase Creek, Scotch Creek, Celista Creek, Reinecker Creek, Hunakwa Creek, and many smaller creeks and streams.   There are 34 inlets into Shuswap Lake and just one outlet.   About 540 lakes, streams, creeks, and rivers contribute to the volume of water in Shuswap Lake.   The total area of Shuswap Lake covers 30, 960 hectares (310 square miles).   The total volume of water in the lake averages about 13.1 cubic km and it all flows out through one outlet, the South Thompson River.