Scientists and the Case of the Slimy Swimming Hole

There’s a chance that this summer you’ve headed to your favorite swimming hole or beach only to see a notice like this:



Water Unsafe for People and Pets

Such warning signs are often unnecessary. The change in the water’s color from clear or blue to brown, green, or red along with an accompanying bad smell is enough to make most swimmers think twice before diving in.

If this has happened to you then you may have the harmful algae bloom blues. Unfortunately, there’s no easy fix to the problem of harmful algae blooms (HABs). However, knowing what’s behind these water changes and what can be done about it can help take the edge off the disappointment – at least enough to formulate a new cooldown strategy. (Ice cream anyone?)

In most cases, the microscopic culprits of HABs are cyanobacteria, sometimes known as blue-green bacteria. Other possible offenders are dinoflagellates, diatoms, and other protozoans.

Cyanobacteria have existed for nearly three billion years. In fact, we may have them to thank for transforming earth to an oxygen-rich planet during the Great Oxygenation Event around 2.4 billion years ago. Today they are a fundamental part of many terrestrial and aquatic ecosystems, a promising resource for renewable energy, and in some cases a health food! However, some cyanobacteria also produce dangerous toxins that threaten human health.

If it’s any consolation, these toxins aren’t intended for us. Cyanobacteria create and release them to kill neighboring bacteria and give themselves a little more breathing room. Unfortunately, after 3 billion years of evolutionary tweaking, these compounds have become both diverse and potent. Some – such as Saxitoxin, Anatoxin-a, and beta-Methylamino-L-alanine – are among the most powerful natural poisons on earth!

Usually, these toxins are found at such low concentration levels that they pose no threat to anything larger than a single cell organism. However, when cyanobacteria populations suddenly surge in size the concentration of these chemicals also skyrocket. At these much higher concentrations, the water can become dangerous to drink or even touch for a prolonged time.

Swimming in or drinking water with a high concentration of cyanotoxins can cause skin rashes, swollen eyes, allergy-like symptoms, and stomach problems in humans. Repeated exposure may also cause permanent liver and neurological damage. For example, beta-Methylamino-L-alanine may be an environmental risk factor for Parkinson’s disease, Alzheimer’s disease, and ALS. Other animals – everything from fish to your faithful fido – risk similar health hazards if they come in contact with cyanotoxin contaminated waters. Consequently, HABs are both a public health concern and an environmental threat.

The bad news is that algae blooms are on the rise. In some areas, they are becoming as predictable a summer event as fourth of July fireworks. They’re also appearing in new water bodies at a rapid rate. It’s important to note that most blooms are non-toxic (ABs rather than HABs). However, the number of HABs is also increasing. This is because many lakes, rivers, and oceans are becoming perfect cyanobacteria habitats.

In order to thrive, cyanobacteria have a few simple needs. They like their waters calm and sunny. They like it warm (65oF or above). And, like most of us, they prefer it when they don’t have to go too far for all their essential nutrients. In the past, these last two requirements have kept cyanobacteria population sizes in check, but recent developments are changing water conditions and removing these limiting factors.  

Across the country (and around the globe), summer temperatures are rising causing many ecological changes. One is that water temperatures are also getting warmer. Toxic cyanobacteria prefer these warmer waters. Higher temperatures also stop many lakes from internally mixing which creates calmer and even warmer waters. Furthermore, as algae populations thrive and grow they themselves make the water warmer. These three factors build off each other to make the water positively hot.

Another cause is phosphorus and nitrogen water pollution. Nutrients may not seem like the worst things to add to water. However, the secondary effects of such contamination can be devastating. High nitrogen and phosphorus levels in the water cause microorganism populations to explode. In some cases, these microorganisms quickly consume all the dissolved oxygen. This creates the water equivalent of a dessert once the oxygen is gone. In other cases, they allow cyanobacteria populations to dominate and destroy the water ecosystem.

Land-use changes are a related problem. When rainwater has time to seep into the ground the process both filters the water and helps it cool down. But when rain waters flow immediately into streams and then lakes the water tends to be both hot and contaminated. This can lead to a high rate of infection between different bodies of water.

So what’s a swimmer to do?

To protect others the immediate solution is to provide timely warnings. Most states have hotlines or websites where the public can report HABs. Scientists are also working on modeling software that will predict blooms. This software uses satellite data but also needs on the ground observations. You can help by downloading this app.

In some cases, algicides can be used to reduce or eliminate the HAB. These must be able to kill most cyanobacteria without permanently poisoning the water. Three popular algicides are silver nitrate, copper sulfate, and sodium percarbonate. Unfortunately, applying these can be prohibitively expensive for larger bodies of water. To address this the company BlueGreen Water is working on a technology that focuses its algaecide on just the surface of the water to limit the amount needed.

However, battling HABs long term will require us to tackle the bigger issues of nutrient water population and climate change. Learning more about these issues, talking to others, and taking concrete actions are three ways forward. To address nutrient water pollution consider building a rain garden to slow down and filter stormwater, switching to nitrogen-free and phosphorus-free fertilizer for your lawn and garden, or volunteering to plant trees and shrubs around local streams and ponds to help filter water and keep the water body cooler. For actions that you can take to reduce greenhouse emissions and help tackle climate change download this climate handprint sheet.