Conservationists believe they have saved the ‘spiritual home’ of the eel in London’s East End—traditionally where cockney jellied eels originated—in their attempts to clean up a polluted River Lea.

Young eels, known as elvers, have been caught in a jam trying to reach their mating grounds in the waters of the Lee Navigation because of river barriers installed over the years to control pollution and the tidal flow.

They make an incredible migration across the Atlantic, through the English Channel, into the Thames and the Lea tributary, after swimming 5,000 miles from the Sargasso Sea around Bermuda.

Now special bypasses for eels have been built at Bow Locks, Three Mills and Lea Bridge Weir to encourage elvers to get through the barriers that obstruct their upstream migration.

This was identified by the Canal & River Trust as “a necessary measure for the recovery of the critically-endangered European eel.”

The young eels are now using the new bypasses, according to researchers from the London Zoo who recorded the first 13 elvers getting through this year.

“The Lea was a heavily polluted waterway,” explained the River Trust’s Leela O’Dea. “It has now been transformed into today’s important wildlife habitat.

“Having elver in the river really is the icing on the cake—what an incredible journey they’ve undertaken, all the way from Bermuda to their spiritual home in the East End.”

The trust has been working with the London Zoological Society and volunteers from Thames 21 environment charity who have been monitoring the eel bypass at Bow Locks for the migrating elvers.

Thames 21 programmes manager Theo Thomas said: “We hope this project helps explain why there has been such a dramatic drop in the numbers of eels.

“We may also discover how many of the 13 elvers recorded at Bow Locks may have made it back out of the Lea to the Sargasso Sea.”

The elvers will live many years in the Lea, slowly maturing before returning to the Sargasso to spawn.

The Lea was historically an industrial river which suffered heavy pollution. Continual improvements have been made, such as installing reed beds, dredging the river, clearing invasive plants to improve water quality and now putting in the bypasses to help young eels get through to their mating grounds.