Pupils at five South Yorkshire primary schools are releasing more than 9,000 eels into local rivers to try and halt a decline in numbers.
The project has been organised by environment charity Don Catchment Rivers Trust (DCRT).
According to the trust, the European eel population in the UK has declined by 95% since the 1980s.
The students were given young eels, known as elvers, to raise in glass tanks at their schools.
'Wriggly and eye-catching'
The trust's project officer, Karen Eynon, said the children have fed them and looked after them for the last four weeks.
"I think they are excited by them," she said.
"They're wriggly and eye-catching. It's not quite the same as raising eggs, you can actually see what's happening.
"So the kids are having a great time raising them and finding out the weird and wonderful things they do."
The trust said that European eels were once common in South Yorkshire rivers.
The eels will live in the rivers for up to 40 years, until they swim across the Atlantic Ocean to their breeding grounds in the Sargasso Sea in the middle of the North Atlantic Ocean.