The River Bush (from the Irish: an Bhuais) is a river in County Antrim, Northern Ireland. The River Bush is 33.5 miles (53.9 km) long. The river's source is in the Antrim Hills at 480m. From there the river flows northwest, with a bend at the town of Armoy. It then flows west, passing through Stranocum, and then bends north, passing through Bushmills before reaching the sea at Portballintrae on the North Antrim coast. It flows through a fertile valley devoted to grassland-based agriculture with limited arable cropping. The underlying geology is basalt and the water is slightly alkaline with magnesium making an unusually large contribution to total hardness. The river supports indigenous stocks of Atlantic salmon and brown trout. Saint Columb's Rill, which is a tributary of the river, is the source of water used for distilling Bushmills whiskey.
The River Bush has traditionally been a salmon-fishing river, though the numbers dwindled in the late 20th and early 21st century. The River Bush still offers excellent salmon fishing. It is managed as a premier salmon river by Department of Culture, Arts and Leisure (DCAL), Inland Fisheries Division. The Department also operates a fish farm and hatchery at the River Bush Salmon Station (which can be visited), providing assistance to the River Bush Salmon Research Project. This project was established in 1972 and is a long term programme of research investigating both the sea water and fresh water phases of the lifecycle of the Atlantic salmon. The research programme has led to the recognition of the River Bush as an index river by the International Council for the Exploration of the Sea (ICES).