A lengthy article concerning the discovery of the toxic by product of cyanobacteria, BMAA, and its potential association with ALS and other neuro degenerative diseases appears in most recent Discover Magazine. the article is not referenced online yet (that I can find). I recall information concerning the neurotoxicity of cyanobacteria more than a decade ago, though these articles mark recent interest into the possibility of implicating BMAA toxin in ALS cases.
http://tpwmagazine.com/archive/2009/july/scout5/

Flora Fact: Blue-Green Mystery
Sometimes found in Texas lakes, cyanobacteria may be the cause of several diseases, but new research could lead to a cure.
By Wendee Holtcamp
... Biologists at the Institute for Ethnomedicine, led by Director Paul Alan Cox, believe they’ve found the culprit for ALS (Lou Gehrig’s disease) and other “tangle diseases” including Alzheimer’s, Parkinson’s disease and supranuclear palsy. The tiny neurotoxic molecule BMAA (β-N-methylamino-L-alanine) is produced by blue-green algae (also called cyanobacteria) found worldwide. The good news? The discovery could lead to a cure. The bad news? BMAA in drinking water could be a health risk even at low levels, but no one’s testing for it in water supplies yet.