Lead exposure testing, Flint water crisis. Close-up of a medical worker testing blood samples at a clinic run by the Genesee County Health Department in Flint, Michigan, USA. The blood testing was made necessary because of the lead contamination of the city's water supply. The drinking water crisis in Flint started in April 2014, caused by lead leached from old water pipes after the supply was switched to more corrosive water from the Flint River. Elevated levels of lead in the blood caused health problems in thousands of children and adults. A public health state of emergency was declared. Photographed on 12 March 2016.