The Anthropocene is characterised by disruption of physical, chemical and biological processes across the planet, with flow on effects to ecosystem structure and function. Biodiversity loss globally has seen a focus on global syntheses and targets for increased protection for species and habitats (www.iucn.org/resources/issues-brief/post-2020-global-biodiversity-framework). Yet, the study of freshwater ecosystem function to underpin biodiversity has received less attention. Global biogeochemical cycles, for example, have been identified as being outside the safe operating space for humanity, with climate change impacts and freshwater water use also of concern, and on a downhill trajectory (www.nature.com/articles/461472a). Research on freshwater ecosystem function has often focussed on simplistic measures such as quality parameters. Therefore, it is critical to examine ecosystem function using methods that are more meaningful, and then scaling them up to appropriate spatial and temporal scales, by combining these studies with new monitoring and modelling approaches. In this talk I provide examples of approaches to understanding ecosystem function, and reconciling spatial and temporal scale. This includes research on cyanobacterial blooms and response to nutrient processes, and the use of process studies and bioassays to link catchment scale and point source impacts to water quality and quantity, with flow on effects to higher trophic levels. These multidisciplinary approaches incorporating laboratory, field and data analysis approaches have provided the means for more effective prediction and management of freshwater systems.