Earthworms are probably not the first iconic species you think of in the context of river health. It’s easy to laugh at the notion that the wriggly pink strings that hide underneath your compost bin are a key part of a functioning hydrological system – and yet they, and the soil they live in, are.

Soil stores, purifies, retains and drains water – regulating its flow to groundwater bodies and rivers alike, and playing a key role in water quality by taking up nutrients or releasing sediment. Like any ecosystem, soil relies on a complex network of interactions between organisms of all sizes, as well as physical and chemical processes, and much more, but earthworms in particular tell us a lot about how our soil is functioning and in turn influence how it behaves.