This photograph of a toxic cyanobacterial bloom has the typical appearance of a thick pool of green oil paint. This bloom occurred in 1981 and was found to consist of species in the genus Microcystis. (W. Carmichael)


Impacts on Aquatic Ecosystems

Ecosystem impacts stemming from the effects of both toxic and non-toxic high biomass cyanobacterial blooms are well documented.  Hypoxic events that suffocate and kill fish and bottom-dwelling organisms are perhaps the most common adverse impact of high biomass blooms.  In addition, blooms can block sunlight penetration into the water column, preventing growth of beneficial algae.  Food web crashes can also result due to the unpalatability and low food quality of many cyanobacteria, which can result in starvation of consumers and their predators.

Cyanotoxins can accumulate in the primary consumers and potentially be transferred up the food web.  Cyanotoxins have been implicated as the cause of mass mortalities of fish and birds and have also been tied to the death of pets and livestock which may be exposed through drinking contaminated water or licking themselves after bodily exposure.  Furthermore, ungrazed cyanobacterial biomass that accumulates as clotted mats pose a particular threat to dogs, who may eat the toxic mats.  For this reason, dog deaths have emerged as an unfortunate early warning that a toxic cyanobacterial bloom is occurring.

Last updated: April 12, 2018