UK ECN site. The River Bush enters the Atlantic Ocean close to the Giants Causeway on the North Antrim coast of Northern Ireland. Rising in the Antrim hills at 480 m OD, for must of its length the river 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, but it is the salmon population which is of the greater interest. Bush salmon have been the focus of long term studies on salmon ecology and on the techniques suitable for managing salmon populations. A fish-trap on the river at Bushmills, some 3.5 km from the sea, enables ascending adult fish and returning juvenile salmon smolts to intercepted, counted and sampled.