In the fall of 1609, several hundred European settlers were struggling to survive on swampy Jamestown Island, riding out a brutal drought and hoping for boatloads of supplies. By the following spring, after a horrific winter that became known as the “starving time,” all but 60 had perished. Four hundred years later, historians can only speculate about the causes of this massive population collapse, which nearly snuffed out the first permanent English settlement in North America. But a team of geologists at the College of William & Mary may be closing in on a suspect: drinking water fouled by salt, arsenic, human waste or a medley of these contaminants.

Life was no picnic for the Jamestown colony’s earliest founders, but at least they had enough to eat. Evidence from waste pits suggests that the settlers, who first arrived on the island in May 1607, feasted on deer, turtles and sturgeon during their first year in the New World, said historian James Whittenburg, the director for instruction at the National Institute of American History and Democracy. (“The sturgeon in the James River were so large that colonists would wade out and harvest them with an axe,” he added.) Thanks to an uneasy truce brokered by their leader, Captain James Smith, they supplemented this high-protein diet with corn received from local Powhatans in exchange for goods.

But in the fall of 1609, shortly after the arrival of new ships packed with more mouths to feed, a disastrous sequence of events plunged Jamestown into famine, said Whittenburg. Faced with their own shortages because of a prolonged drought, the Powhatans cut off trade with their neighbors after Smith returned to England for medical treatment in October. The settlers began taking food by force, and the Powhatans retaliated by laying siege to Jamestown; confined to their fort, the colonists could no longer hunt, fish or seek fresh water. “We do see in the trash bins from the ‘starving time’ that they’re eating really small animals,” said Whittenburg. “They eat up all of the domestic stock—the dogs and the horses. They get down to eating rats and even poisonous snakes.”...