Water temperature is a critical variable in rivers because, as temperature increases, the water’s capability to hold dissolved oxygen drops. At the same time, warmer water increases the metabolic rate of aquatic organisms, thereby increasing their oxygen consumption. As temperatures rise at lower elevations and incoming solar radiation increases toward the Equator, lowland rivers in subtropical and tropical regions are prone to overheating during low-flow seasons. Therefore, identifying areas where natural physical and biological processes protect fish from climate change, known as “thermal refugia”, is pivotal for freshwater fish conservation. Our lab investigates the drivers of thermal heterogeneity in southern lowland rivers and how fish interact with thermal refuges.