One of the worst North American outbreaks of E. coli has hit the small town of Walkerton, Ontario, presumably because water supplies were contaminated by runoff from nearby cattle feedlots after a heavy rainstorm on May 12. Five people have died and nearly 1,000, or about a fifth of the town’s population, have fallen ill from the intestinal bacteria. Civic officials have been accused of covering up the problem rather than quickly alerting the public. The case is highlighting the problems of factory-farm pollution and contamination of water supplies in agricultural areas. Ontario’s environment minister yesterday announced stricter regulations for testing at water plants and public reporting of problems.