Cyanobacterial (blue-green algae) blooms are occurring more frequently in freshwater lakes and along coastlines. They are often due to nutrient enrichment of the lakes, especially nitrates and phosphates, caused by human activities. Cyanobacteria grow faster at warmer temperatures. The thick masses of cyanobacteria absorb so much light that the water temperature increases. The algae at the base of the aquatic food webs prefer cooler temperatures and cannot compete successfully with rapidly growing cyanobacteria in the warmer temperatures. Microcystis, Nostoc, and Anabaena are examples of cyanobacteria that cause blooms as well as release neurotoxins. This category of blooms is referred to as Harmful Algal Blooms (HABs). They can occur in drinking water and survive typical water purification processes.