Some cyanobacteria have the capacity to produce toxins dangerous to human beings. Toxins can be found either free in the water where the bloom occurs or bound to the algal or cyanobacterial cell. When the cells are young (during the growth phase), 70 to 90% of the toxins are cell bound, whereas when the cells Cyanobacteria have been largely studied in fresh water systems, due to their ability to proliferate, to form massive surface scums, and to produce toxins that have been implicated in animal or human poisoning.Some species of algae may also contain toxins, but incidents where fresh water algae are at the origin of cases of human or animal illness have very seldom been reported.Coloured toxic tides caused by algal overgrowth have been known to exist for many centuries. In fact the Bible (Exodus, 7: 20-24) states "all the water of the Nile river became red as blood and fish which were in the river died. And the river was poisoned and the Egyptians could not drink its waters.Algal blooms were observed in 1638 by fishermen in north west of Iceland. Fjords were reported to be stained blood red and during the night produced a kind of phosphorescence. The fishermen thought that the colours could be due to the blood of fighting whales or to some marine insects or plants (Olafsson and Palmsson, 1772). The first scientific report of domestic animals dying from poisoning as a consequence of drinking water that was affected by a blue/green algae bloom was in 1878 in lake Alexandrina, Australia.