The dipper is Britain's only aquatic songbird, diving in fast streams for invertebrates and providing a sensitive welfare indicator for upland river ecosystem health.
Acidification of upland streams from atmospheric deposition reduces invertebrate prey communities dippers depend on. Liming of acidified catchments has allowed recovery in some areas. Sewage and agricultural pollution in lowland reaches affects wintering birds. Pollutant bioaccumulation causes eggshell thinning and reproductive failure in contaminated catchments.