The settlers did not know that New Zealand’s native fish had evolved in isolation for millions of years without large visual predators living in their waterways.Native galaxiids, including dwarf galaxias, roundhead galaxias and flathead galaxias, were poorly prepared for the arrival of such a powerful predator.The effects of brown trout were rapid and severe. Even where rivers have no physical barriers, trout in middle sections can prevent native fish from moving between high-country spawning areas and downstream habitats.The impact of brown trout goes beyond native fish. New Zealand’s Our Fresh Water 2017 report identifies trout as an important cause of native fish declines, but recreational fishing remains protected and managed by regional Fish and Game councils.