How can we use a modelling approach to predict the movement of waterborne bacteria and viruses, especially in a notoriously tricky coastal location? This is the challenge a team from Bangor University is facing, along with colleagues from water and subsurface specialists Deltares, Istituto Superiroe di Sanità (ISS) and the University of Exeter.The 55 km-long River Conwy (Afon Conwy) rises in the moors of Snowdonia, widening into the Conwy Estuary near Conwy itself before flowing into the Irish Sea. It’s a well-known beauty spot and tourism destination; however the river and its catchment (the surrounding area where rainwater collects) have a long history of microbiological pollution. With shellfisheries on the Conwy as well as recreational activities, the risk of impact on public health is high.