<P> The Great Lakes contained 21% of the world's surface fresh water around the year 2000: 5,472 cubic miles (22,810 km), or 6.0 × 10 U.S. gallons (2.3 × 10 liters). This is enough water to cover the 48 contiguous U.S. states to a uniform depth of 9.5 feet (2.9 m). Although the lakes contain a large percentage of the world's fresh water, the Great Lakes supply only a small portion of U.S. drinking water on a national basis . </P> <P> The total surface area of the lakes is approximately 94,250 square miles (244,100 km)--nearly the same size as the United Kingdom, and larger than the U.S. states of New York, New Jersey, Connecticut, Rhode Island, Massachusetts, Vermont, and New Hampshire combined . </P> <P> The Great Lakes coast measures approximately 10,500 miles (16,900 km); however, the length of a coastline is impossible to measure exactly and is not a well - defined measure (see Coastline paradox). Of the total 10,500 miles (16,900 km) of shoreline, Canada borders approximately 5,200 miles (8,400 km), while the remaining 5,300 miles (8,500 km) are bordered by the United States . Michigan has the longest shoreline of the United States, bordering roughly 3,288 miles (5,292 km) of shoreline, followed by Wisconsin (820 miles (1,320 km)), New York (473 miles (761 km)), and Ohio (312 miles (502 km)). Traversing the shoreline of all the lakes would cover a distance roughly equivalent to travelling half - way around the world at the equator . </P> <P> It has been estimated that the foundational geology that created the conditions shaping the present day upper Great Lakes was laid from 1.1 to 1.2 billion years ago, when two previously fused tectonic plates split apart and created the Midcontinent Rift, which crossed the Great Lakes Tectonic Zone . A valley was formed providing a basin that eventually became modern day Lake Superior . When a second fault line, the Saint Lawrence rift, formed approximately 570 million years ago, the basis for Lakes Ontario and Erie were created, along with what would become the Saint Lawrence River . </P>

When did pollution in the great lakes start