Great Lakes Island, Harsens Island, Manitoulin Island, and the Toronto Islands. As of 2007, four car ferry services cross the Great Lakes, two on Lake Michigan: a steamer from Ludington, Michigan, to Manitowoc, Wisconsin, and a high speed catamaran from Milwaukee to Muskegon, Michigan, one on Lake Erie: a boat from Kingsville, Ontario, or Leamington, Ontario, to Pelee Island, Ontario, then onto Sandusky, Ohio, and one on Lake Huron: the M.S. Chi-Cheemaun runs between Tobermory and South Baymouth, Manitoulin Island, operated by the Owen Sound Transportation Company. An international ferry across Lake Ontario Rochester, New York, to Toronto ran during 2004 and
Great Lakes U.S. side highlight five large municipal systems (those of Detroit, Cleveland, Buffalo, Milwaukee and Gary) as being the largest current periodic sources of untreated discharges into the Great Lakes. Algae such as diatoms, along with other phytoplankton, are photosynthetic primary producers supporting the food web of The Great Lakes. The changes in the size or in the function of the primary producers may have a direct or an indirect impact on the food web. Photosynthesis carried out by diatoms comprises about one fifth of the total photosynthesis. By taking CO2 out of the water, to photosynthesize, diatoms help to stabilize