Wildlife on the river
Look across a typical dale from a moor-edge viewpoint and the course of the beck in the dale bottom is only given away by the twisting line of alder trees hugging its banks. However, go down into the dale and find a bridge or a footpath along the riverbank and you might be lucky enough to spot a dipper – a small brown bird with its bright white bib – sitting on a rock above the water, or a bright blue flash as a kingfisher flies by.
Clean water is essential for the teeming numbers of invertebrates that support the river food chain. Many nationally important species also depend on our healthy rivers. For example, otters and water vole live on rivers throughout the North York Moors National Park, although you are unlikely to see either. The National Park Authority works with partner organisations to protect and enhance water vole populations, in particular.
The River Esk is important as Yorkshire's principal sea trout and salmon river, and the fishery forms a crucial part of the local economy. The Esk also supports a dwindling population of freshwater pearl-mussels, the last such surviving population in Yorkshire. The Pearl Mussel and Salmon Recovery Project seeks to reverse this decline.
Meanwhile, on the upper part of the River Derwent white-clawed crayfish are found. This is the only native species of crayfish in Britain, but it is under threat from non-native species, such as the aggressive plague-carrying signal crayfish.