Sometimes ambergris washes up on shores. Anyone who finds it can get pretty wealthy all of a sudden. But these "sea snot" algae outbreaks are so disappointing and gross by comparison. You definitely won't mistake one for the other.

Lake Erie, partly in Canada and the USA, has this intermittent seasonal problem. It is mainly attributed to a certain soft drink company that takes but does not give back to the local environment. Their operations heat up the water, turning nearly 1/4 of the entire Great Lake into green sludge every year.