Special river "ladders" are being used in parts of Wales in an attempt to halt a decline in the eel population.
The Environment Agency Wales said eel numbers had fallen by 95% in recent years.
Experts claim the snake-like fish is unable to reach certain habitats, partly because it cannot pass man-made weirs.
The ladders are brush-like in design and provide eels with the grip to climb up and pass weirs that block their way.
They have been fitted in rivers in Carmarthenshire, Ceredigion and Bridgend.
But the Environment Agency is also looking at other measures to help the fish and may introduce new laws to protect from over fishing.
The population in the northern hemisphere has seen a dramatic fall since 1970.
It is believed numbers have dropped to 5% of historic European eel stocks. The agency said some estimates had this figure closer to 1%.
Project leader at Environment Agency Wales, Stephen Carter said: "Eels are an important part of the wildlife in our rivers and we have seen an alarming decline in recent years.
"Part of the problem is they cannot get past the man-made weirs that were built during our industrial past.
"Now, using these special ladders, they can get past these weirs and reach the wetlands and habitats upstream where they can mature and thrive."
According to experts, the reason behind the eel's decline largely remains a mystery due to the difficulty in tracking the fish during its migration.
The spawning habits of the eel is the exact opposite of the other migratory river users - the salmon and the sea-trout which migrate upstream to spawn.
Eels, however, swim out to the Sargasso Sea, in the North Atlantic, to reproduce.
The young eels, called glass eels when they are at sea, are then carried by the Gulf Stream and reach river systems across Europe.
Mr Carter added: "We are working to improve access, restock rivers and control how many are taken and hope to see their numbers grow.
"Eels are a major part of the diet of wildlife like otters, herons and bitterns and form an integral part of the Welsh ecosystem."
The agency said eels were not only a key part of the ecology of Welsh rivers, but also provided an income to 250,000 fishermen across Europe.