The River Esk is a river in North Yorkshire, England that empties into the North Sea at Whitby after a course of around through the valley of Eskdale, named after the river itself. The river's name is derived from the Brythonic word "isca" meaning "water". The Esk is the only major river in Yorkshire that flows directly into the North Sea; all other watercourses defined as being major rivers by the Environment Agency, either flow to the North Sea via the River Tees or the Humber Estuary. Overview Due to its rural nature, the river is clean and healthy, supporting a wealth of wildlife. Salmon spawn right up through Eskdale, and a number of "leaps" are provided to enable them to travel through weirs on the course. There are clearly visible examples at Ruswarp, where the tidal stretch through to Whitby begins and at Sleights. Around Whitby the Esk has a large population of sea trout, and the river is noted for freshwater pearl mussels (the only river in Yorkshire to have them), although these are threatened with extinction due to buildups of silt in the river. In 2021, conservationists removed the mussel colony into a specialist facility to encourage the mussels to release their young, which can be raised in a secure safe environment, before the mussels are then all put back. The Esk is also the only major river in Yorkshire to drain directly into the North Sea. The river rises at the Esklets on Westerdale Moor in the North York Moors. The Esklets are actually three moorland streams that combine in Westerdale to form the River Esk. The river flows through Westerdale before merging with a large number of becks from the surrounding hills, including Tower, Baysdale, Sleddale, Danby, Great Fryup, Stonegate, Glaisdale and Murk becks. Running east through the valley known as Eskdale it leaves the moors via the villages of Sleights and Ruswarp, between which it forms the boundary of the North York Moors, and reaches the North Sea three miles later by bisecting the resort of Whitby. Partway down the river at Danby Bridge, there is a ford in which vehicles can get trapped. Between the junction of Fryup Dale and Lealholm the river passes through a narrow, steep-sided and wooded valley known as Crunkly Ghyll. Here the river drops from the valley above to reach the village. Crunkly Ghyll was formed during the