Rivers are large running waters created mainly by natural processes but often greatly altered by centuries of human activity.
We treat waterbodies shown on UK Ordnance Survey 1:25,000 maps with two blue lines as rivers: this refers to waters with a channel width of more than 8.25m. People often assume that rivers are just their permanent channels: in fact virtually all rivers would naturally also have a floodplain area where water flows intermittently – although this fact is often forgotten, or ignored.
Where are they found?
There are about 90,000 km of rivers in UK, and they are found in all parts of the country.
What can you find living in a river?
Naturally, the plants and animals living in rivers differ according to how steep and fast flowing the river is, and whether it has predominantly acid or alkaline water. In many places pollution also has a big impact on what lives in rivers with many species eliminated, or their populations reduced.
Rivers support the plants and animals that need running water – for animals this means species that depend on constantly high oxygen levels – like stoneflies and many (but not all) mayflies – and filter feeders, like blackflies or net spinning caddis larvae, that depend on moving water to bring their food to them. In the river margins, even in quite fast flowing upland rivers, there are also many of the ubiquitous freshwater plants and animals that are not too fussed where they live, as long as there is water. Plants like water mint and brooklime fall into this group, as do animals like the Common Water Slater and the Wandering Snail. All rivers should have a good variety of fish in them – and in Britain this would naturally include both coarse and salmonid fish. Rivers don’t have as wide a variety of water beetles as ponds, nor so many submerged water plants. Rivers do have specialist dragonflies and damselflies – like the White-legged Damselfly or the Club-tailed Dragonfly which are only occasionally found in riverside ponds.
Why are they important?
Rivers are important because they can be amongst our richest freshwater habitats, and support species that absolutely depend on permanent running water – salmon and other fish that need clean gravels to spawn on, stoneflies and mayflies that depend on constant high oxygen levels and cool water, river mosses, the invertebrate eating Dipper and in the very best upland rivers, Pearl Mussels.
What we’re doing to help
We will be mapping the most important rivers for freshwater wildlife to encourage efforts to protect or improve their water quality – the main threat faced by rivers. We’ll undertake projects to protect endangered species living in rivers, where others are not already doing this work. We’re also undertaking research to find out what techniques work best to protect rivers from pollution.
We’ll be undertaking projects to restore river floodplains – most conservation effort at present concentrates on river channels but this is the one part of the river which is usually still present. Floodplain wetlands – which are also part of the rivers – have been eliminated from large parts of the British landscape. We expect there will be a better result for biodiversity by working on these restored wetlands – particularly if they can be kept separate from the polluted water in the rivers – rather than making small interventions in the channel, and research suggests this is indeed the case.