A river in north Wales which was hit by a major pollution incident three years ago has been replenished with 5,000 fish.
Thousands of fish were killed in the River Dee
More than 100,000 fish were killed in the incident - the cause of which remains a mystery - on the River Dee in July 2000.
The river is one of the most regulated and controlled in Britain.
It is important - not just for its beauty or fishing - but as a source of drinking water for nearly three million people in both north Wales and England.
The Dee is a river which attracts a lot of tourists so the better the health of the river, the better for the local economy
Environment Agency spokesman
Four thousand fish were released at Eccleston Ferry outside Chester and a further 1,000 were released in Farndon on Friday.
A spokesman for the Environment Agency said they had been refilling the river for some time.
"In 2001 we put in 150,000 fish including all different species at various places in the River Dee," he said.
"It is important to refill the river because fish are very good indicators of river water quality, they are sensitive to changes including oxygen depletion.
"The Dee is a river which attracts a lot of tourists so the better the health of the river, the better for the local economy."
Scientists still do not know why the fish died nearly three years ago.
The agency said the case "remains a mystery" but it was still open and it was hoped they would discover the cause eventually.