What impact might mitigation of diffuse nitrate pollution have on river water quality in a rural catchment?

► A rapid risk assessment of river phytoplankton growth is presented. ► A river nitrate model sensitive to land management is presented. ► Riparian trees better suppress phytoplankton blooms than reducing nutrient inputs. ► Even the most drastic nutrient limiting strategies will not greatly curtail blooms. ► Interventions should be focused in areas with the longest river travel times.