Eel passes like this one at Oath have proved a great success
Research carried out in a Somerset river has given fresh hope to a once-common fish that is now listed as "critically endangered".
The number of European eels in British rivers has fallen by 95% in 20 years.
Research carried out by the Environment Agency (EA) in the River Parret found sluices and gates in waterways were stopping the fish migrating to breed.
Now, a new law requires eel passes - special narrow steel tubes - to be fitted on affected waterways.
The eels can wriggle their way up the passes, on a bed of bristles, to reach the other side of a barrier.
Although the eels spend most of their adult lives in European rivers, they have to reach the Sargasso Sea off Bermuda in order to spawn.
Environment Agency eel expert Andy Don said: 'We know that even one eel pass in the right location can have an instant effect.
"Two passes installed along a watercourse that flows into the River Parrett in Somerset saw 10,000 eels queuing up to use them on the first night, and both 2008 and 2009 saw around 40,000 eels using the passes each year."
The EA says more than 100 new gates, which only cost £200, are being fitted at other locations across the country.