Industrial agriculture now accounts for over half of America's water pollution. Two years ago, Pfiesteria outbreaks connected with wastes from industrial chicken factories forced the closure of two major tributaries of the Chesapeake and threatened Maryland's vital shellfish industry. Tyson Foods has polluted half of all streams in north-western Arkansas with so much faecal bacteria that swimming is prohibited. Drugs and hormones needed to keep confined animals alive and growing are mainly excreted with the wastes and saturate local waterways.