Abstract: In 1937 a group of elite Pākehā men from Auckland were caught fishing on Rotoaira, a remote highland lake in which trout fishing was, uniquely, reserved for Ngāti Tūwharetoa. These men used their arrest to have the law reserving the lake for Māori fishers neutralized in court. While by the end of the following year the government had created a new stronger law, this incident was the culmination of a longer debate about trout fishing that shows the larger importance of questions of environmental management to settler colonialism in Aotearoa New Zealand. Early twentieth-century attempts by Pākehā to control and claim fishing rights in Rotoaira show that animal management (especially through acclimatization) and fishing as sport was an engine of colonization. Debates over fishing on this remote lake illustrate a larger aspect of colonization where settler claims to authenticity and control overrode or attempted to override Māori kaitiakitanga.