The Nashwaak River located in west-central New Brunswick, Canada; is a tributary of the Saint John River. It is 113 kilometres long. The river rises from Nashwaak Lake (southeast of the village of Juniper) and flows south and east through uninhabited land and rapids to the village of Stanley. From Stanley, the Nashwaak flows southeast to Nashwaak Bridge and Taymouth, then south the through several rural communities such as Durham Bridge, the historic town of Nashwaak Village and Penniac before it reaches the town of Marysville. It flows into the Saint John River opposite downtown Fredericton.

The river's name comes from the Maliseet language, a corruption of the word for slow current. It was used heavily by the Maliseet people as a transportation route to northwestern New Brunswick. A French fort, Fort Nashwaak, was built at the river's mouth in 1692 (near present day Barker's Point, New Brunswick) and was the first European settlement in the Fredericton area. It was captured by the British in 1696, and land along the river was later granted to United Empire Loyalists during the American Revolution. Further settlement occurred through the 19th century. A rail line and Route 8, both important links from southern to northern New Brunswick, were built along the river's shore. The rails were removed in 1995 and it is now a walking trail.