Beginning in August 1820, two teams of surveyors, including British explorer and cartographer David Thompson, mapped the area of St. Joseph Island, Drummond Island, and Lesser and Greater Manitou Islands (today Cockburn Island and Manitoulin Island). Mapping this corner of Lake Huron was a challenge given how little was actually known about the shores and depths of the channels between the islands. The agent for the American survey team, Major Joseph Delafield complained "No map that I have seen has any truth as it respects the position of Drummond’s or the other islands about St. Marys. We entered this bay without a pilot, but are told we cannot proceed up river without one."