Shock new evidence shows scale of plastic pollution in our rivers

Caddis fly larvae have been found using plastic in chalk streams the River Thet and Pakenham Stream in Norfolk and Suffolk.

Where the diverted River Thet now meets the Little Ouse. Picture: Conor Matchett (Image: Archant)

Environmentalists fear the discovery could have devastating long-term consequences for our rivers.

For the inch-long caddis, which grow into sedge flies when they mature, are at the bottom of the food chain and are eaten by everything from fish to birds and bats.

Bottom feeders like bream can devour them whole and crunch through their casings with their powerful throat teeth.

A caddis fly which has included a piece of blue plastic in its protective case (Image: Thetford River Group)

Brown trout rise for the flies as they hatch. Fish which have ingested plastic could be eaten by larger predators such as pike or even otters.

Plastics find their way into rivers via wastewater, untreated sewage run off and litter left on the banks.

Helen Baczkowska, acting conservation manager for Norfolk Wildlife Trust, said: "Fewer than 300 chalk streams exist on earth, 85pc of them in England. With several fine chalk streams, including the magnificent Wensum, Norfolk is globally important for their protection.

An Otter feeds on a Roach in the River Little Ouse in Thetford. Photograph Simon Parker (Image: Archant)

"Chalk streams are both precious and vulnerable. They support a host of scarce wildlife, including water vole, otter, wild brown trout, white-clawed crayfish, bullhead and many invertebrates.

"But most of our chalk streams are in poor health. They are threatened by water abstraction, pollution from farming and sewage, and a host of contaminants which we casually flush away from our daily lives."

The caddis were found by the Thetford River Group, which samples insects to monitor the aquatic environment. Members also carry out regular litter picks using kayaks.

Clare Higson, Sean Ready and Clare Miller-Jones from the Thetford River Group after a litter pick. (Image: Ella Wilkinson)

Volunteer Clare Higson said: "It's something I'd read about and known about in other parts of the world but it's shocking to see it in a local chalk stream.

"The swans, the ducks and the kingfishers don't take them out of their cases, they just swallow them whole.

"One thing would be for people to take their plastic home and not leave it by the river."

An Environment Agency spokesman said: “We do occasionally see microplastics in caddisfly cases, although this isn’t something we routinely monitor."

They added: "We do not have enough data on microplastics and Caddisfly larva to give a definitive answer on its effects on either the developing larva, or other species that eat it."