Cyanotoxin which is why they are usually green or blue. Cyanobacteria are found almost everywhere; in oceans, lakes and rivers as well as on land. They flourish in Arctic and Antarctic lakes, hotsprings and wastewater treatment plants. They even inhabit the fur of polar bears, to which they impart a greenish tinge. Cyanobacteria produce potent toxins, but they also produce helpful bioactive compounds, including substances with antitumour, antiviral, anticancer, antibiotic and antifungal activity, UV protectants and specific inhibitors of enzymes. Cyanotoxins are often implicated in what are commonly called "red tides" or "harmful algal blooms". Lakes and oceans contain many single-celled
Great Lakes steamships, they were called "steamboats"—the same term used on the Mississippi. The ships also have a distinctive design (see Lake freighter). Ships that primarily trade on the lakes are known as "lakers". Foreign boats are known as "salties". One of the more common sights on the lakes has been since about 1950 the 1,000‑by‑105-foot (305-by-32-meter), self-unloader. This is a laker with a conveyor belt system that can unload itself by swinging a crane over the side. Today, the Great Lakes fleet is much smaller in numbers than it once was because of the increased use of overland freight, and a