- Lifespan
- 2–3 years in the wild
- Size & Weight
- 12–15 cm body length; 10–16 g
- Habitat
- Fast-flowing, clean streams and rivers with dense bankside vegetation and rocky substrates, occasionally found in ditches and canal systems.
- UK Distribution
- Found throughout much of mainland Britain north to central Scotland, though absent from Ireland and southern coastal areas; resident year-round.
- Diet
- Aquatic invertebrates including freshwater shrimp, insect larvae, small fish, and aquatic worms; hunts by diving and walking along the riverbed.
- Prey
- Freshwater shrimp (Gammarus), mayfly and caddisfly larvae, bloodworms, sticklebacks, water boatmen
- Predators
- Owls (particularly Barn Owls), herons, pike, cormorants, and foxes
- Mating Season
- April to August
- Breeding
- Two litters per year; 5–8 young per litter; gestation period approximately 21–22 days; young weaned at 4–6 weeks.
- Behaviour
- Highly aquatic and active both day and night; uses venomous saliva (toxic to small prey) to subdue invertebrates. Solitary and territorial, marking territory with scent glands. Can dive for up to 30 seconds and carries an air bubble in its fur for insulation.