Running Waters

Scotland has a huge resource of running waters, from torrential mountain burns to meandering lowland rivers. These support an impressive wealth of aquatic and marginal habitats and species. As well as providing key services for people, such as water supplies and recreation, running waters also serve vital roles for biodiversity, providing water to our freshwater lochs, estuaries and wetland habitats, and acting as wildlife corridors through Scotland's rural and urban landscapes.

What are running waters?

The term 'running waters' includes any surface water that flows, from tiny mountain trickles to the mighty Tay, which has the highest mean flow of any watercourse in Britain. Factors such as geology, soils and climate have a major influence on the form, substrate, water quality and flow of running waters, as described in the Scottish Rivers section. The diverse permutations of these that occur in Scotland result in a rich mosaic of habitat types varying both within and between watercourses. With aquatic and riparian (bank-side) vegetation adding further diversity, habitat is available for a wide range of associated wildlife including mammals such as water voles and otters , birds such as dippers, numerous invertebrates, and freshwater fish.

From the hills to the sea

In mountainous or upland areas, running waters are typically steep with a bed of rock, boulders and cobbles, and with rather sparse plant growth, notably of mosses and liverworts. With fluctuating flows due to heavy precipitation or snow-melt, the habitat supported by such headwaters is constantly changing. The flora and fauna tends to be dominated by a relatively small number of species adapted to unstable environments, such as stoneflies and other riverflies.

At lower altitudes, shallower channel gradients and more reliable flow result in more stable habitats and a greater abundance and diversity of aquatic species that requires less dynamic environments, such as the freshwater pearl mussel . Deposits of riverine shingle and sand support a varied flora and fauna including rare insects and spiders. Increasing amounts of riparian vegetation create subtle changes in flow and energy, as for example where erosion occurs round the roots of bank-side trees. The resulting accumulations of fine sediment support species such as lampreys.

Nutrient levels typically increase with increasing distance downstream, and the lower and more sluggish-flowing reaches of watercourses support a higher abundance of aquatic plants with species such as water-crowfoots, water-starworts and alternate water-milfoil. These provide seasonal cover for fish, and marginal habitat to support the adult phase of insects such as damselflies, whose larval stage is wholly aquatic.

Why are our running waters important?

Scotland holds two thirds of Britain's river systems, supporting economically important species such as Atlantic salmon and globally rare species such as freshwater pearl mussel. Migratory fish such as salmon and sea trout rely upon the presence of different habitats along the length of watercourses to support their various life stages. The lifecycle of the freshwater pearl mussel is inextricably linked to that of salmonids, and so it too is indirectly dependent upon the availability of a diverse range of habitats. It is this habitat diversity and the species which it supports that makes Scotland's running waters so important both nationally and internationally.