river

The government said its reforms to bathing water rules will help further, but campaigners said that swimming in England's rivers was still too often risky to health.

California depends on just a few strong atmospheric river storms to provide moisture; as little as five to seven can end up being responsible for more than half of the year’s water supply, he said.

The remainder often runs into rivers and coastal areas, contributing to oxygen-depleted "dead zones" that harm aquatic ecosystems.

Taking place over the last couple of months, the team has been searching and identifying species at both known and potential river sites in boroughs such as Newham, Richmond upon Thames and Barnet.

"We're fearful, every time it rains it's like a river down here. My wife is on edge, she's not sleeping."