A recent column called Snipets from Science compiled by Paul Burton in the Peninsula Pulse (volume 17 issue 26) reveals the potentially deadly effect of rotting algae on animals and man. The following article comes from the pages of Science, August 19, 2011.
Near Brittany, France, algal blooms caused by excessive farm runoff end up as slimy masses along a picturesque beach. Recently 36 wild boars were found dead along such a beach, and their death has been attributed to hydrogen sulfide gas produced by the rotting algae. Angry farmers denied culpability, but autopsies confirmed death by hydrogen sulfide poisoning. In 2009 a horse in the area died of hydrogen sulfide poisoning, and there is evidence a truck driver who was removing dead algae also died from inhalation of the gas.