Understanding biodiversity change and addressing questions in freshwater management and conservation requires access to biodiversity data and information. Unfortunately, large, comprehensive data sources on freshwater ecology and biodiversity are largely lacking. In this chapter, we explain how to take advantage of secondary data and improve data availability for supporting freshwater ecology research and biodiversity conservation. We emphasise the importance of secondary data, give an overview of existing databases (e.g., taxonomy, molecular or occurrence databases), discuss problems in understanding and caveats when using such data, and explain the need to make primary data publicly available.