Fish Lens

Fish Lens

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Fish Lens

Over 10% of our freshwater and wetland species are threatened with extinction and at least two-thirds are in decline. If we don’t act now to save freshwater we risk losing these species altogether.

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Freshwater species

Here are some of the wild fish we work to protect, click on a species to find out more about them. Our work has a particular focus on Atlantic salmon as a keystone species and indicator of river health.

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    Atlantic Salmon

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    Brown Trout

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    Sea Trout

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    European Eel

Atlantic salmon are famous for an epic migration that sees them swim up rivers and leap waterfalls over three meters high. Once a common sight in our waters, only a quarter of UK rivers supported viable populations of wild Atlantic salmon in 2022.

Extraordinary transformation    

Atlantic salmon are an indicator of the health of our rivers. Like all wild fish, they need clean, flowing and productive water to grow successfully.

Most Atlantic salmon are anadromous. This means that they are born in freshwater rivers, and then migrate to the sea to grow big on a rich ocean diet. Eventually, they return to the very river where they were born to reproduce.

The Atlantic salmon has many different names at different points in its life. Alevin, fry, parr, smolt, post-smolt, grilse, and kelt are all names for different stages of the salmon’s life cycle, with distinct appearances and traits adapted to the conditions they find themselves in.

A perilous and unforgiving journey  

On a journey that will see them cover 1,000 of miles, this incredible species will encounter many dangers that threaten its survival. One of which is the devastating impact of open-net salmon farming in Scotland. Poorly run and badly sited open-net salmon farms put wild salmon at risk from parasites (notably sea lice) and diseases. Farmed fish can also escape and threaten the genetic integrity of wild salmon, compromising their future survival.

As their journey continues, Atlantic salmon will come up against barriers in the form of weirs and dams that prevent them from swimming upstream, pollution from sewage and agriculture that devastates water quality and the impacts of climate change that increase water temperature and reduce flow.

Helping protect wild Atlantic salmon

There’s lots that we can do to protect wild Atlantic salmon.

Our Off the Table campaign calls on the hospitality sector to take farmed salmon off its menus. Engaging chefs, restaurants, and food critics, Off the Table raises awareness of the environmental, sustainability and welfare issues with farmed salmon.

You can help too by refusing to eat farmed salmon – small changes make a big difference.


The brown trout is the only native trout species in the UK and is one of the most genetically and physiologically diverse vertebrate (an animal with a backbone or spinal column) species in the world which means it can adapt to many different environmental conditions.

One fish, many faces  

The brown trout remains in freshwater habitat for its entire life. There are many different populations of the same species, each with its own life cycle, appearance and diet. In fact, brown trout vary so much across their populations that some question if it is even one species!

Changing habitats

Brown trout need cool, well-oxygenated water and variable conditions to complete its life cycle.

Human alteration of river channels and man-made structures, along with water pollution are threatening UK populations.

Brown trout are a popular fish for fly fishing and because of this, it has been introduced well beyond its native range around the world, even as far as New Zealand. This can have devastating effects for local ecosystems.


The brown trout and the sea trout are two distinct forms of the same species. Sea trout migrate to the sea, adapting to a marine environment, before eventually returning to reproduce in the river in which they were born.

Surviving at sea

All brown trout are genetically capable of migrating to sea to become sea trout, but only some of them will make this migration. Often the majority of sea trout in a river will be female while males are more likely to be brown trout.

Many sea trout do not feed in freshwater habitats, sometimes going months living just on the reserves they built up in the sea. Approximately ¾ of sea trout are able to return to sea after spawning and enter another reproductive cycle despite these long periods without feeding!

Dangerous journeys

The sea trout is under threat.

In Scotland, where marine habitat overlaps with open-net salmon farms, sea trout are continually exposed to parasites and diseases which threaten their survival and can make them less able to reproduce when they return to freshwater habitat.

Without action, the iconic sea trout may be completely lost from our waters.


The grayling has an unusual scientific name. “Thymallus” reportedly comes from the Greek for “thyme smell”, because a freshly caught grayling has a faint smell of thyme. Widespread throughout Northern Europe, it is migratory, but only within freshwater.

Lady of the Stream

Grayling are distinctive because of their large and colourful dorsal fin, which is more prominent in males than females.

Grayling use different river habitats at different life stages. Young grayling are not strong swimmers and prefer slower-moving water near the bank of a river, while adult graylings need fast flowing, well-oxygenated, clean water found in the centre of the river channel.

Sensitive to pollution

Grayling are particularly sensitive to pollution and need well-connected habitats and good water quality to complete their life cycle.


Shad are in the Herring family. There are two species of shad in the UK, the Twaite Shad and the Allis Shad. The allis shad is generally larger than the twaite shad, but they are very difficult to distinguish as they look almost identical.

Rare and precious

In 2015 there were only four known breeding populations of twaite shad in the UK, with both twaite and allis shad considered some of the rarest fish in the country.

Shad, like Atlantic salmon and sea trout, are anadromous. They return from the sea to spawn in freshwater rivers in spring. Almost all Allis shad only spawn once before dying, which happens at night, splashing about loudly. In contrast, it is estimated that about 25% Twaite shad survive for a second breeding cycle.

At risk of extinction

Both the Twaite and Allis shad are threatened with extinction in the UK and have extensive legal protection with several special areas of conservation (SACs) designated for their protection.

The declines seen in shad populations are caused primarily by barriers to migration and water pollution in rivers.


For many years the European Eel was a mystery because, despite being a popular food source, fishermen never saw young eels and did not know where they came from.

Fascinating and elusive

All European eels are born in the Sargasso Sea. Found in the Atlantic Ocean, surrounded by strong currents collectively called the North Atlantic Gyre, the Sargasso Sea is the only sea with no land borders!

After spawning, the young eels travel in the gulf stream to UK rivers as tiny larvae, transforming into a transparent glass eels when they enter estuarine waters, a coastal water body where fresh and saltwater mixes. This journey can take three years.

European eels usually live for 5-20 years but one eel was reported living to the age of 155 in a well!

Critically endangered

The European eel is critically endangered and experiencing dramatic population declines across its geographical range.

This decline has been linked to many different threats including barriers to migration, climate change, parasites, and pollution.


Wetland habitats

Many habitats make up a river system. Click on the wetland habitats below to find out more about the spaces that wild fish need to survive.

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    River corridors and riparian habitats

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    Coastal and intertidal zones

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    Chalk streams

Headwaters are the permanently flowing streams that feed a river system. Typically, they extend up to 2.5 km from the source. 

A large river system will have many streams that feed into it over its length. These are also known as tributaries. 

70% of the river network in England is made up of small streams. They have diverse conditions depending on the geology, altitude, and land use in the surrounding landscape. 

Headwaters are important for biodiversity.  

1. Species transport

Headwaters are important to the whole river system as they allow species to be transported down river and establish populations in the lower reaches. 

This is a vital function when the lower reaches of a river lose species because of pollution.

2. Macroinvertebrate communities

Macroinvertebrates play a vital role in the ecology of river and stream ecosystems. They transfer organic matter from a variety of sources through the food web.

A third of a river system’s macroinvertebrate biodiversity can only be found in the headwaters.

Why are headwaters particularly vulnerable?

1. Low water volume

Headwaters are particularly vulnerable to agriculture because they have a low volume of water.

2. High concentrations of pollutants

The low water volumes limit the dilution effect. Pollutants or sediment that pass into the stream will be at a high concentration.


A river corridor is the area of land that a river influences. This includes the river channel and any land to either side, such as wetlands and floodplains.

The riparian zone is the land beside the river that is affected by the presence of the river. Riparian habitats include specialised plant and soil communities that can tolerate being partially or totally underwater. 

Natural riparian habitats have an important role in maintaining river health.

Riparian forests and floodplains can reduce flooding, reduce transmission of sediment and pollution into rivers, sequester carbon and keep river water cool.

Riparian habitats are under pressure from modern intensive agriculture

65% of floodplain zones are now occupied by intensive agriculture and 99% of rivers have had their riparian habitat altered by agricultural land use. 

1. Changing land use

The land bordering rivers and streams is being altered to create agricultural land. Riverbanks are modified and channels are straightened reducing the length of a river by up to 50%.

2. Removal of important bankside habitat features

Submerged root systems, ponds, and rivulets are damaged when riverbanks are modified.

Riverbank modification also changes flow regimes and destroys habitat for juvenile fish, macroinvertebrates, and birds.

3. Low water availability

Riparian vegetation is very vulnerable to low water availability. Loss of this habitat reduces the diversity of the invertebrate community, as well as the total abundance.


The coastal zone is where the land meets the sea. The intertidal zone is the area of land between the low tide and the high tide.

Coastal and intertidal habitats face diverse pressures

Erosion, sea level rise, ocean acidification, and pollution are all at play. These habitats and the wildlife that they support are also vulnerable to disturbance by people.

Why do coastal and intertidal zones need protecting?

1. Species diversity

The intertidal zone supports important biodiversity including seagrass meadows, saltmarshes, mudflats, and rocky beaches.

The UK’s seagrass meadows capture carbon worth up £5.3m.

2. Defence against coastal erosion

Mudflats and saltmarshes are an important defence against coastal erosion and support unique communities of plants and animals.

It is estimated that protection by coastal wetlands instead of sea walls saves up to £4,600 per metre of coastline.

3. Special habitat for rare and endangered species

Species that live in this habitat need to be able to survive being submerged by the sea when the tide comes in and completely dry when the tide goes out.

The specialist plants that live here are known as halophytes because of their ability to survive in salt water, and many of these are rare and endangered because they can only be found in these special habitats.

4. Breeding ground

Coastal habitats in the UK provide globally important breeding grounds for many migratory birds.


The marine environment covers 71% of the earth’s surface.

The seas and oceans that make up this environment contain many diverse habitats and lifeforms.

The factors threatening our marine environments

1. Chemical and plastic pollution

Freshwater sources run into the sea and many of the problems of chemical and plastic pollution in freshwater impact the marine environment too.

2. Climate change

Climate change is having a disproportionate effect on the oceans, warming them at an alarming rate. This temperature rise is causing ocean acidification.

All these significant changes are affecting marine species. Many are changing where they live or experiencing population declines.

The marine environment supports freshwater and terrestrial life.

1. Marine phytoplankton

These tiny photosynthesising plants and bacteria produce up to 50% of the world’s oxygen. This is despite having only 1% of the biomass of all the terrestrial plants on earth. 

2. Feeding grounds

Marine environments are important feeding grounds for species like Atlantic salmon and sea trout.

These salmonid species rely on the marine food that is only available outside of the rivers they are born in to grow to a size that helps them breed successfully.


Over 75% of the world’s chalk streams are found in England and they support lots of important wildlife. They are often referred to as England’s rainforest.

Chalk streams are a globally rare and important habitat.

England’s chalk streams support a genetically distinct population of Atlantic salmon which have adapted to the specific environmental conditions provided. 

The clean water allows chalk streams to support populations of many sensitive species of macroinvertebrates.

Chalk streams flow from underground chalk aquifers through landscapes dominated by chalk. This generates beautifully cool, clean, and clear water.

Winterbourne chalk streams are areas that only have flowing water for part of the year, known as ephemeral streams. These support both terrestrial and aquatic species over the course of the year.

Why do chalk streams need protection?

1. Over-abstraction

Chalk streams provide over 70% of the drinking water in the Southeast of England and are vulnerable to over abstraction.

2. Pollution

Over-abstraction concentrates pollution within the river. Reducing the volume can warm the stream to temperatures that are damaging for species present including salmonid eggs.


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