‘Is it seaweed – or something more sinister?’ The sewage blighting Cornwall’s beaches

‘We realise there’s very little we can do’ … Gail Muller, left, with Lyn Pollard at Swanpool beach in Falmouth, Cornwall. Photograph: Jonny Weeks/The Guardian

It has become a grim but necessary part of the routine for sea swimmers who splash out into Falmouth Bay from Gyllyngvase and Swanpool beaches, two sandy stretches of Cornish coast separated by a brambly headland at high tide and sparkling rock pools at low. They pack costumes, goggles, towels, perhaps a flask of tea – and then pause to check the Surfers Against Sewage (SAS) app, to establish whether it is clear to swim or whether they might find something nasty in the water.

“Sad that we have to do that, isn’t it?” says Gail Muller, 44, a writer, teacher and adventurer who loves to swim in the ocean all year round, as she sits with her puppy, Bill, gearing up for a dip.