Algae in water, usually obvious by the presence of an agal bloom indicated by a green, yellow-brown or red scum on the surface, is potentially very dangerous. Harmful agal blooms (HABs) are those produced by harmful phytoplankton and are not easy for non-experts to differentiate from less dangerous blooms. The phytoplankton that produces a bloom can be in concentrations of billions of cells per litre of water and can give off dangerous toxins. Depending on the type of algae present, drinking contaminated water can lead to an array of illnesses including in some cases paralysis and death.
Furthermore, blooms in fresh water are usually the result of an abundance of phosphorus from agricultural runoff and thus indicate potentially high levels of fertilizer contamination which can cause ‘blue baby syndrome’ and be fatal to babies.
Though it is generally easy to identify contaminated water because of proximity to agricultural land or golf courses and evidence of the bloom itself, assessing the dangers is very difficult and water with algal blooms is not easily treated using conventional methods and should be avoided at all costs.