Toxic algae blooms are thought to play a role in humans developing degenerative neurological disorders such as amyotrophic lateral sclerosis and Parkinson's disease.
Less than one percent of algal blooms produce hazardous toxins, such as microcystins. Although blue-green or other algae do not usually pose a direct threat to health, the toxins (poisons) which they produce are considered dangerous to humans, land animals, sea mammals,  birds and fish when the toxins are ingested. The toxins are neurotoxins which destroy nerve tissue which can affect the nervous system, brain, and liver, and can lead to death.