Summary: Climate change is rapidly changing the availability of water across the landscape, posing a critical threat to freshwater ecosystems and services. Yet, our current understanding of the consequences of changing hydrology for production and resilience of freshwater ecosystems is limited. A critical missing link for assessing how changes in streamflow impacts diverse habitats and ecosystems is limited monitoring in headwater streams that serve as the water towers of North America. Moreover, we lack empirical information on the relationships between water availability and species response and resilience. This talk shares several projects across the northern Rocky Mountains where USGS ecohydrology science is leading the way toward understanding critical relationships to inform water use and coldwater fish conservation to better support ecosystems in the future.