Searching Hampshire river for Britain's fastest-declining mammal

"We get very excited by flattened poo," is a sentence I was not expecting.

Neither was I expecting to be standing thigh-high in a chalk stream surrounded by people armed with poles wearing waders and lifejackets.

"Found another," cries a volunteer with their head in a river bank.

Reserves officer for Central Rivers and Downs with Hampshire and Isle of Wight Wildlife Trust, Andy Reeves, grins and updates his chart.