The Mersey River is a river in Nova Scotia which flows from Lake Kejimkujik in Kejimkujik National Park, then through Lake Rossignol to empty into the Atlantic Ocean at the town of Liverpool, Nova Scotia.

The river was a major transportation route for the Mi'kmaq people of Nova Scotia. Later, it was used to transport logs out of the interior of the province. Now, there are a number of hydroelectric projects on the river.

Tributaries of this river include the:

• Shelburne River
• West River
• Little River