Drying rivers are widespread and diverse in cool, wet countries such as the UK. Here, the chalk streams of southern England are among the UK’s most iconic rivers, and their ‘winterbourne’ reaches naturally experience seasonal dry phases. These winterbournes support biodiverse aquatic and terrestrial communities, including important populations of nationally rare specialist insects. Although celebrated for their high water quality, biodiversity and provision of recreational ecosystem services, chalk streams are also subject to a breadth of human impacts including eutrophication and geomorphological degradation. In addition, climate change and water abstraction are artificially increasing the spatial and temporal extent of their dry phases. River managers thus need tools to assess the ecological health of winterbourne chalk streams regardless of whether they are wet or dry. We will present insights from research done by academic and stakeholder collaborators to enable biomonitoring in dry rivers. Using newly collected field data, we will evaluate plant and invertebrate communities—including both their terrestrial and aquatic species—as biomonitors that enable ecological health assessments during dry phases. We call for global testing, adaptation and use of our approaches to promote dry-phase biomonitoring as a key part of holistic aquatic–terrestrial biodiversity assessments done in drying rivers around the world.