Aotearoa New Zealand has pristine mountain rivers and lakes, but downstream in the lowlands our rivers are some of the most polluted in the world. Nutrients, sediment and human pathogens are pouring from farms into waterways, causing damage to ecosystems and threatening human health. Dr Mike Joy speaks with the Policy Observatory’s Keri Mills on the nature of the crisis in our lowland freshwater ecosystems, its historical and political causes, and the policy changes that are needed to improve the situation.