Kākahi are a keystone species in lake and river ecosystems, keeping the water clean by filtering one litre of water every hour. These native mussels once blanketed lakebeds across Auckland – but recent surveys found an alarming decline and disappearance across many lakes. A team of scientists and divers have mounted a rescue mission for one of the last remaining kākahi populations, trying to keep the mussels safe from invasive fish through all the steps of their complicated – and fascinating – life cycle. …