Small running waters, a vital network for wildlife

Streams are small running waters mainly formed by natural processes, although they are often substantially modified by human activity.

What is a stream?

We define steams as waterbodies shown on UK Ordnance Survey maps as a single blue line, representing waterbodies less than 8.25 metres wide. They are distinguished from ditches in:

  • Usually having a sinuous, winding form
  • Not following field boundaries – or if they do, pre-dating boundary creation
  • Showing a relationship with natural landscape contours, for example running down valleys

Streams don’t always have water in them. It is quite natural for the first part of any stream to be seasonal, depending on the year. The headwaters of streams sometimes naturally dry out, creating a different but valuable aquatic environment. In hot parts of Europe, for example, temporary streams have highly specialised assemblages of endangered species, including fish.

Stream running through a forest.

- Stream in Dartmoor National Park, Devon


of streams in England


of headwater streams east from the Humber to the Dorset coast are biologically degraded


of streams in England


of headwater streams east from the Humber to the Dorset coast are biologically degraded

What can you find living in a stream?

Streams support a range of plants and animals that depend on running water, as well as freshwater species that can be found more or less everywhere. Pristine, clean, unpolluted streams can be important nursery grounds for Trout and Salmon. They’re often home to the Bullhead as well.

In some parts of southern England, small streams may be the last refuge for Native Crayfish that have otherwise been wiped out by crayfish plague. The surprisingly large larvae of the Golden-ringed Dragonfly are typical of small acid streams.

Species directory
Shallow water flowing fast down a rocky stream on a hillside, trees behind.

- Headwater stream in Scotland.

Why are streams important?

Streams are important because they make up the majority of the running water environment – the length of streams is much greater than larger rivers. They are a vital for network for the plants and animals that need this habitat, including young Salmon and Trout, Lampreys, Native Crayfish, the Golden-ringed Dragonfly and Cool Water Stoneflies.

In many parts of the landscape, streams are more likely to be unpolluted than bigger rivers.

Our policy work
Small stream on moorland.

- A headwater stream starting in a pond, Lake District

How Freshwater Habitats Trust is helping streams

We carry out much of our conservation work at catchment scale. Therefore, we focus on protecting the whole water environment, including the streams, right down to the smallest of headwaters.

In different parts of the country, we are mapping freshwater wildlife and water quality in a range of habitats, including streams. Through our catchment work and research projects, we are working with landowners and partners to evaluate the benefits of natural flood management measures, such as leaky dams, tree hinging and debris dams on rivers and streams.

Streams are also a crucial element of our strategy to create the Freshwater Network.

The Freshwater Network
Debris dam on a river.

- Debris dam on the River Leck

Find out more about our work on streams

New Forest wetland on a wintery day with blue sky
New Forest catchment partnership

We’re protecting the New Forest’s high quality freshwater habitats – including its pristine headwater streams.

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Aerial view of a landscape, including a meandering river and newly dug ponds.
The Freshwater Network

Through the Freshwater Network, we’re creating wilder, wetter, cleaner, connected habitats to reverse the decline in biodiversity.

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Pond with tree reflected on the water, blue sky behind.
Water Friendly Farming

We’re evaluating the effects of different management techniques on streams to assess the effects of freshwater biodiversity and for natural flood management services in this farmed landscape in Leicestershire.

Find out more