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Slimy Summer Swimming: Harmful Algal Blooms in Lakes, Rivers and Streams

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You may notice a green, red or brown film on your favorite boating or swimming area in the summer. This coloring could mean that the water is affected by harmful algal blooms. USGS scientists Dr. Barry Rosen, Dr. Jennifer Graham and Dr. Keith Loftin discuss why these blooms can be harmful to people, animals, and ecosystems, as well as what the USGS is doing to better understand the problem.




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[Intro Music]

Kara Capelli: Hello and welcome to USGS CoreCast. I'm your host, Kara Capelli. Have you ever noticed a green film of algae on your favorite swimming spot in the summer? Today we're going to be discussing harmful algal blooms: why they can be harmful to people and animals and what the USGS is doing to better understand the problem. We'll be talking with three USGS scientists who study this issue. Dr. Barry Rosen is a phycologist, or a scientist who studies algae. Dr. Jennifer Graham is a limnologist, or a scientist who studies lakes and Dr. Keith Loftin is a chemist and environmental engineer. Thank you all for being here.

Barry, let's start with you. What is a harmful algal bloom?

Dr. Barry Rosen: Well, harmful algal blooms are an accumulation of these very small organisms known as algae. They happen in fresh water, coastal areas and in the ocean. If you look at a water body it may look bluish-green to you or even reddish, or sometimes even a brown color.


Sometimes it even looks like paint, but if you look at it closely you'd see small floating specs which are little colonies of algae that make up the bloom. They're most noticeable in the surface of the water body but also appear below the surface. The blooms are fed by nutrients and the nutrients can come either from the land surrounding the water - that happens a lot of times when people fertilize their lawn and too much fertilizers put in. It also can be from nutrients that are in the sediments that are regenerated and then feed the bloom.

Cyanobacteria is a specific type of algae, and they're responsible for most of those freshwater harmful algal bloom. They're a natural part of the food web and are eaten by, you know, many simple animals and some fish. They only become a problem when you get massive accumulations and they're not being consumed then we have a bloom occurring.

Kara Capelli: Jennifer, Barry was just talking about cyanobacteria and you study some of the toxins associated with it. Besides being a nuisance and unsightly are these algal blooms actually harmful to humans?


Dr. Jennifer Graham: Yes, they can be. Probably the most immediate concern surrounding the cyanobacteria are that the toxins that they produce can be very toxic to aquatic and terrestrial animals including aquatic life, pets, livestock and people. In humans, exposure to these toxins range from skin rashes to severe stomach upset to seizures or even, in extreme cases, death.

Kara Capelli: So if I'm out in the lake or from on a boat and I see what I think is a harmful algal bloom, what should I do?

Dr. Jennifer Graham: Probably, the best thing to do is just avoid that area. The cyanobacteria do produce taste and odor compounds that can smell bad and so if you're approaching an area and you can really smell an earthly or musty smell, and it's prevalent, that's also a good indicator that you may want to avoid the area that there may be an issue of cyanobacteria.


Another good thing to do is notify local authorities responsible for the affected area such us state health department, lake manager, or relevant state agencies.

Kara Capelli: Keith, you're an environmental engineer, let's turn to you for this next one. What are people doing to clean up the blooms?

Dr. Keith Loftin: Some of the short-term lake management practices that have been used include aeration and mixing algaecides, dyes to reduce sunlight penetration, and sediment dredging to remove nutrients. All of these really have limited success in controlling harmful algal blooms. They can be quite costly and may have other undesired effects. Some of the longer-term solutions people are trying include sediment nutrient management in the watershed. This is a large endeavor and also a lengthy endeavor.

Kara Capelli: Barry, let's get into the USGS science surrounding this issue for just a little bit. What makes cyanobacteria blooms toxic?


Dr. Barry Rosen: Well, the cyanobacteria produce a couple of different classes of compounds; cyanotoxins or cyanobacterial toxins. They cause liver damage so they're hepatotoxins or they cause nerve damage, they're neurotoxins.

Kara Capelli: Jennifer, you were talking earlier about taste and odor compounds. Tell us a little bit more about taste and odor compounds. Are those different from cyanotoxins?

Dr. Jennifer Graham: Well, the taste and odor compounds are another group of chemicals that are produced by the cyanobacteria. There are no known human health effects associated with the taste and odor compounds, but they can really be aesthetically displeasing and drinking water utilities spend a lot of money removing these chemicals from drinking water.

Kara Capelli: So, Keith, what is the USGS doing to study taste and odor compounds, as well as cyanotoxins?

Dr. Keith Loftin: USGS approach to these issues has been three-fold mainly.


First, we developed standardized methods that enable us to reliably measure cyanobacteria, their toxins and taste and odor compounds in our streams, lakes and reservoirs. Second, we conduct studies that help us determine the potential human and ecological risk posed by cyanobacteria and their toxins to people and animals. Third, having two-way communication with the public is a necessary part of this puzzle to make sure we are addressing real problems that our community is facing.

Some of USGS' preliminary work has included a couple of surveys to characterize the amount and types of toxins of taste and odor compounds occurring in lakes and reservoirs. USGS has also been working on a taste and odor reservoir model to predict when taste and odor events are likely to occur. These types of models are extremely useful when they work, because they allow drinking water utilities to minimize the amount of these chemicals in tap water.

Kara Capelli: Well, Jennifer, Keith and Barry, thank you for this great information and thank you so much for being here today.


Dr. Keith Loftin: Thank you, Kara.

Dr. Barry Rosen: Thank you very much.

Dr. Jennifer Graham: Thanks Kara.

Kara Capelli: For more information about specific USGS studies and activities relating to cyanobacteria, you can visit ks.water. Don't forget to follow the USGS on Twitter at or visit our other social media channels at

This CoreCast has been a product of the US Geological Survey, Department of the Interior. Thanks for listening.


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