Observer: The St. Clair River at Sarnia is no longer playing a major role in falling water levels in the upper Great Lakes, a new study says. The document, released Friday, debunks the so-called ‘bath tub’ explanation that some scientists and environmentalists have been theorizing about for years. According to the theory, massive dredging in the river by the U.S. Army Corps of Engineers in the early 1960s created a ‘drain hole’ through which water is being lost, much like when a plug is …