Glaciers gouged out the 5 Great Lakes, creating the biggest lake system on the planet, containing 6 quadrillion gallons, or one fifth of the world's freshwater supplies. Their total shoreline, including islands and channels, extends for some 10,900 miles (17,549km), more than the US West and East coasts combined! The sheer size and concomitant fetch of these lakes explain the presence of surprisingly large, surfable waves with the right weather conditions. Because the system extends over 700mi (1120km) from W to E and 500 miles (800km) from N to S, a surf experience on the NW shore of Lake Superior can be vastly different from a session on one of Erie's southeastern beaches. First Great Lakes surfer was a GI returning from Hawaii with a longboard in 1945, but surfing really started to grow on the eastern shore of lake Michigan and north-eastern shore of Lake Erie from 1963/64. Despite poor consistency (about 10 surfable days per month in season) and often inhospitable conditions, there are more freshwater surfers joining the line-ups each year.