A cultural health index (CHI) for streams was developed in a program of collaborative research involving members of Ngai Tahu (an iwi [tribe] within the South Island of New Zealand) and ecologists at Otago University. The aim was to provide a tool for effective participation of Maori in resource management decisions. Five cultural values are of central importance to the nature of the CHI: mauri (spiritual life force), mahinga kai (traditional resource harvesting), kaitiakitanga (guardianship obligation), ki uta ki tai (mountains-to-the-sea holistic philosophy), and wai taonga waters that are treasured). The CHI has three components. Forty-six stream sites in two culturally important river catchments were first classified according to whether there is a traditional association with Maori. The second component assessed the historical and contemporary mahinga kai status of the site, including questions of legal and physical access. The third component was a Cultural Stream Health Measure (CSHM) that encapsulates indicators of catchment, riparian, and instream condition in a manner that is consistent with Maori values. The CSHM was found to be significantly correlated with “western” measures of stream health commonly used in New Zealand (Macroinvertebrate Community Index, Stream Health Monitoring and Assessment Kit), and performed at least as well in encapsulating the relationship between land development and stream health. We describe a multistep process by which other indigenous people can develop a cultural ecosystem health measure, and then use the tool to ensure a substantial role in decision making with the agency in charge.