A LARGE salmon has been filmed swimming near the viewing window at the Diglis Fish Pass.

The video, shared by the Unlocking the Severn team, shows the fish stopping to linger in front of the window before darting back behind the wall, leaving its tail on display. 

Salmon are just one of the many species of fish that have been observed at the Diglis Fish Pass.

Other species that had made appearances at the viewing window include the endangered twait shad and sea lampreys (also known as vampire fish).

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According to Unlocking the Severn, salmon tend to spawn in November and December in redds that they burrow into gravel substrate in the shallow upper reaches of rivers.

Salmon are not randomly distributed in our seas, but rather follow very narrow migration routes around our coastline to reach their North Atlantic feeding grounds.

The Diglis Fish Pass contains a room below the River Severn, with a large viewing window where fish can be seen making their way upstream.

Two cameras are stationed in the viewing room, with both monitoring every fish which passes through.

The viewing window is illuminated with a backlight so that the cameras can detect fish at all times of the day.

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What is the purpose of a Fish Pass?

The purpose of a fish pass is to allow fish to move past manmade blockages in water. In Diglis, the weir means that many fish looking to travel upstream struggle due to the two-metre separation.

The pass consists of 11 small pools, each just 20 cm higher than the last, making it more manageable for the fish to swim through.

The fish detect the stream of water in the river and can travel upwards, with walls in each pool relieving some of the force created by the water. 

The Diglis Fish Pass relies on volunteer staff who provide tours that can be booked via the Unlocking the Severn website.

For more information on ticket availability, you can visit the Unlocking the Severn website at www.unlockingthesevern.co.uk.