'Each one is like a coral reef in an agricultural desert': One man's mission to rewild the swimming pool

As the group gathers for coffee on a shady terrace at David Pagan Butler’s smallholding deep in the north Norfolk countryside on one of his popular one-day pool courses, he recounts how an early effort was almost scuppered by his son Theo putting sticklebacks in the pond. ‘Fish will wreck it,’ he explains, ‘because they eat all the Daphnia —water fleas that you need to eat the algae.’ (His USP is the crystal-clear water of his pools; of which, more later).

To deal with the sticklebacks, Theo fished a pike out of the river and released it into the pool, ‘which gave a certain edge to swimming’. David made one of his idiosyncratic videos about it for his YouTube channel (120,000 subscribers) ‘and someone shopped me to the Environment Agency’. The officer who duly visited was ‘supportive, b