The Kennebecasis River is a 95-kilometre tributary of the Saint John River in southern New Brunswick, Canada. Its name derives from the Mi'kmaq "Kenepekachiachk," meaning "little long bay place." The river originates in the foothills of Albert County near Goshen, flows southwest through Penobsquis and Sussex, and ultimately joins the Saint John River at Millidgeville. It drains a watershed of approximately 1,346 square kilometres, encompassing portions of the Caledonia Highlands, an extension of the Appalachian Mountains.

The lower reaches of the river, between Sussex and its confluence with the Saint John, pass through a well-defined river valley. This section includes notable features such as Minister's Face on Long Island near Fairvale, a geological formation visible from the water, with hiking access to the top for views across the Kennebecasis Valley. The Brothers Cove and Tucker Park area near the lower river is characterized by Devonian-age rock formations and some of the deepest waters in the system, which has been described as an underwater fjord. Wildlife commonly observed along the river includes bald eagles, loons, cormorants, and white-tailed deer, including piebald individuals. Atlantic sturgeon, salmon, striped bass, shad, smallmouth bass, and brook trout are present in the watershed, and harbour seals are occasionally seen in the lower reaches.

Access points include Fairvale on the Kennebecasis River and areas around Darlings Island, where the Hammond River joins the main stem. The river is accessible year-round, with spring (April and May) offering views of flooded floodplains, summer providing calmer paddling conditions, and early fall notable for foliage colour. Water conditions on the main Kennebecasis can be choppier than on tributary streams such as the Hammond River.

Fishing regulations on the main stem include a fly-fishing-only rule after July 1st and a catch-and-release, fly-fishing-only section in effect throughout the trout season from April 15 to September 15. Paddlers should be aware that the river corridor also hosts Route 1 and the Canadian National Railway line between Sussex and Saint John. Rental equipment and guided tours are available through several outfitters in the Saint John region, and Paddle Canada instruction is available locally for both canoe and kayak paddlers.