The water shrew, Britain's largest shrew, depends on clean fast-flowing streams and is highly sensitive to water quality deterioration and habitat loss.
Water shrews have among the highest metabolic rates of any mammal relative to their size, meaning food shortage causes rapid physiological stress and death within hours. Habitat degradation through pollution, bank erosion and dredging removes the bankside vegetation they depend on for shelter and the invertebrate communities they prey on. They are sentinel species for riparian ecosystem health.