Goopy Green Algae: A Summer Water Hazard

Jul 2, 2019

Credit Falling Havens / Flickr

It seems like every summer it happens, once it’s warm enough to swim, authorities are warning people to stay out of the water. Why? An abundance of one of the simplest living things on earth: algae. Actually a specific type of algae called cyanobacteria, tiny microorganisms that can cause serious illness.  


Keith Bouma-Gregson is an environmental scientist with the California State Water Resources Control Board. He also co-leads the Fresh Water Harmful Algae Bloom Program, and has been tracking blooms in California.  

Keith Bouma Gregson

While cyanobacteria usually make the news when there’s a harmful bloom, it turns out they’re pretty common and can be found across the globe.   

“They’ve been on Earth for a couple billion years,” Bouma-Gregson said. “Often times they persist at a pretty low biomass—there’s not too much of them in any given place—but under certain conditions they can form blooms in lakes and rivers and reservoirs.”  



Cyanobacteria, Clear Lake 2017
Credit State Water Resources Control Board

Again, cyanobacteria are normally kept in balance, but stagnation, warmth or an excess of nutrients—whether from chemical fertilizers, leaky septic tanks or flocks of birds—can spark a bloom, Bouma-Gregson said.  

“Not all of them produce toxins,” he said. “So just because you see it in your fish tank it may not be a toxin producing species.”  

But if it is—watch out.  


Harmful Algae Blooms—referred to as HABs—can affect animals, which is why warnings are often targeted at dog owners who might be inclined to let their dog take a dip on a hot summer day. 


“Usually an animal would have to be ingesting cyanobacteria cells, so water that has a pretty dense bloom in it, and there’s many different types of toxins,” he said. “They tend to either effect the skin—so they might create rashes or irritations—or they will affect the liver, or they will affect the neurological system.”  


Bouma-Gregson said if an animal gets a big enough dose, it can be lethal. He also noted that these types of blooms are becoming more common around the world.  




July 1, 2019 image capture of the State Water Resources Control Board's HAB incident Report Map.
Credit State Water Resources Control Board

“Globally the trend does seem to be that we’re seeing an increase in frequency of these cyanobacterial blooms,” Bouma-Gregson said. “In California we started formally tracking some of these reports a few years ago at the State Water Boards, but certainly it seemed like during the drought that we saw more blooms that were occurring in the springtime and even over the course of the winter.”     


On the positive side, as quickly as they appear, these blooms can dissipate.  


If you have plans for Independence Day or coming weekends involving a waterway, Bouma-Gregson recommends checking this statewide map for any current Harmful Algae Blooms before heading out.