Understanding toxic algae: A deadly phenomenon

Do you remember the episode of The Simpsons where toxic waste from the Springfield Power Plant leaked into Nuclear Lake, accidentally creating Blinky the three-eyed fish and other monstrosities? Well unfortunately this cartoon wasn’t far off from real life. 

Today, more than a half of the world’s rivers are polluted. Pollution (including pharmaceutical pollution), industry and urban development are the main culprits. The impact we have on rivers is a big problem for the environment and human health. When a rivers’ balance is disturbed, toxic algae can bloom freely, allowing bacteria and parasites to flourish, killing wildlife. The results can be devastating. 

Rivers are vital ecosystems

Healthy river ecosystems are crucial for both people and wildlife. Many plants, animals, humans and insects depend on rivers for drinking water. Every drop of water we drink connects us to a river system somewhere in the world. 

In the U.S., water from rivers, lakes and groundwater flows from intake points into treatment plants before it’s pumped into our homes. Our reliance on rivers extends to transportation too. For many communities, rivers provide a vital lifeline for trade, travel and tourism. 

Rivers are critical to the health and survival of millions of species in surrounding ecosystems. This makes rivers biodiversity hotspots. Nutrients and minerals will travel thousands of miles along river systems. These support forests, wetlands and other habitats full of important plants and wildlife. They also support the growth of healthy algae and other plants that form the base of the food chain for a variety of fish species and aquatic life.

A big problem for our rivers is when pollutants from factories and construction sites along riverbanks seep into our vital waterways. That’s because it increases the levels of certain nutrients in the water such as nitrogen and phosphorus. This causes certain algaes to grow quickly, creating a toxic environment for fish and other aquatic species.  

Also called harmful algae blooms (HABs), toxic algae develops when sewage and waste gets into rivers. This upsets the balance of nutrients and minerals, allowing these blooms to grow. This is a problem because they deplete oxygen and block the sunlight that other organisms need to survive. Some HAB-causing algae release dangerous toxins that are deadly to animals and humans.

HABs are found all over the world, and can usually be distinguished by a blue-green or even red color that’s concentrated in one area. The most common organisms that cause toxic algae are cyanobacteria (sometimes called blue-green algae), dinoflagellates, and diatoms (sometimes called microalgae or red tide).

Not all algae is toxic or bad. Algae is the common name for a hugely diverse array of aquatic, photosynthesising (meaning they get their energy from the sun) organisms which produce oxygen — vital for sustaining life. However, not all HABs are poisonous; some are just a nuisance, look weird and smell bad but do not produce toxins… we still wouldn’t recommend drinking or bathing in any lake or river that’s infected.

Toxic algae is a global problem

In Europe, toxic algae has had a big impact on fish populations and water quality. In 2022, the Oder river experienced a mysterious disaster along the German-Polish border. Millions of fish were killed and washed up along the river shore. The cause? Discharge from industry raised the river’s salt concentration and can largely be traced back to the mining industry.

This discharge led to the blooming of golden algae, an organism that normally only exists in salty water and does not belong in the Oder. This algae created neurotoxins that poisoned the fish and created a toxic environment in the Oder river system. What’s worse is that the algae will bloom again if the conditions are right.

In the United States, an enormous outbreak of toxic algae blooms occurred in New York State’s Finger Lakes. All 11 Finger Lakes were affected by HABs outbreaks, which is especially problematic for the more than one million people who depend on the lakes for their drinking water… So what can we do about it?

Is there a solution?

Monitoring and early detection is the best way to help take action against harmful algae blooms. Technology such as remote sensors and real-time water monitoring systems can also help identify when nutrient levels in the water are off so that blooms can be mitigated before they get out of control. 

If they do get out of control, there are some ways to control the spread. At specific frequencies, ultrasound can control algae growth. Without getting too scientific, the algae uses gas vesicles to stay at the water’s surface during the day. This is where they photosynthesise. At night, they sink, using oxygen and nutrients under the water to produce biomass. Ultrasound can create a sound layer in the upper water layer, effectively drowning the algae so it cannot return to the surface. 

Another method to help curb the spread of toxic algae is to use special chemicals. These aquatic herbicides are usually copper-based compounds used to control algal blooms once they have gotten out of hand. However, these chemicals are expensive and require regular dosing in a specific area to not upset the ecosystem further. 

But by far the best ways to combat the knock-on effect of HABs is through river rewilding initiatives that give biodiversity the chance to fight back. Rewilding encourages the return of damaged biodiversity to river systems and promotes natural competitors to the algae.

Projects like the Rewilding Oder Delta are helping give fish in the Oder River and the damaged ecosystem a boost. By replenishing the riverbeds with the gravel stones, fish are encouraged to breed. The project also helps form habitats for new plant and animal species… and that’s just the beginning! Small actions like this can make a big difference to an area’s biodiversity, building a stronger and more resilient ecosystem for the plants and animals that rely on it.

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