Harmful algae blooms: examples from around the world

Overfertilization, other sources of water pollution, and warmer climates are leading to global problems from algae blooms, toxic cyanobacteria, and ecological imbalances

Harmful algae blooms are becoming a more serious problem across the U.S. and indeed around the world. Consider these few impacts:

• 27% of lakes in the U.S. pose a high or moderate risk for potential exposure to algae toxins, based on measured cyanobacteria cell count.
• $4 billion each year is the economic impact of freshwater algae blooms in the U.S.
• $800 million dollars is the value of an estimated 40,000 tons of salmon choked to death by a surge in algae in Chile’s waters in early 2016.

According to the EPA, scientists predict that climate change will have many effects on freshwater and marine environments. When combined with nutrient pollution, harmful algal blooms might occur more frequently, in more water bodies, and to be more intense. Algal blooms are known to endanger human health, the environment and economies.

A scientific paper portrays the  scale of the global algae challenge. In the early 1990s, 54% of Asian lakes, 53% of European lakes, 48% of lakes in North America, and 41% of lakes in South America were all subject to eutrophication, the term that describes an abundance of nutrients that causes accelerated growth of algae. An analysis of satellite data shows that the situation has worsened over the past 30 years in 68% of large reservoirs.

Overfertilization and environmental stress is only making it worse

The key point from the paper is that algae problems are primarily caused by an overabundance of nutrients from excessive use of fertilization. Everybody wants a green lawn, but the phosphates and nitrates in fertilizer promote the growth of algae as well as grass. When rain washes it off lawns and fields, it travels to nearby bodies of water, where the algae are waiting. Very little additional nutrients—on the order of 30 parts per billion—are needed to kick off excessive algae growth. 

Algae on the surface can create an ugly, smelly, dangerous nuisance. But it doesn’t stop there. As it dies it contributes to the layer of sludge on the bottom that would normally be broken down by bacteria of its own accord. The problem is, excess algae above starves the water of oxygen, so normal bio-processes are prevented.

The only long-term solution is to eliminate the causes of excess nutrients. Yet too many people turn to the “band-aid” of using chemicals, particularly copper sulfate, to try to kill algae. As it does that, it also kills good bacteria that aid in digesting the bottom sludge, making a feedback loop that only increases the amount of nutrients in the body of water. Furthermore, some algae can become resistant to the chemicals, necessitating the need for more chemicals, at which point it can become dangerous, even fatal to other aquatic life.

The algae control problem playing out across the world

This scenario is playing out in water sources in the U.S. and around the world, with severe health, environmental and economic impact.

Lake Erie, U.S. freshwater algae bloom

In 2014, residents of Toledo, Ohio learned that their water supply had become toxic, and they were advised not to drink it or even touch it. A freshwater algae bloom in Lake Erie made up of cyanobacteria or blue-green algae shut down local water sources. Such harmful algae blooms have become more common and more toxic every year since the 1990s. In addition to improving water treatment plants, Ohio put in place strict controls to start limiting fertilizer agricultural runoff from surrounding farms.

Lake Taihu, China cyanobacterium bloom

In May 2007, a massive cyanobacterium bloom overwhelmed a waterworks that supplies Wuxi city on Taihu’s northern shore, leaving more than 2 million people without drinking water for a week. To reduce pollution of nitrogen and phosphorus, the region forced hundreds of small chemical and manufacturing plants near Taihu to close or relocate. They also instituted strict monitoring of remaining factories and built sewage treatment facilities on Taihu’s tributaries and is dredging tributary mouths to remove nutrient-rich sediments.

Lake Victoria, Africa cyanobacteria bloom

Africa’s Lake Victoria, the second largest freshwater lake in the world and chief reservoir for the Nile River, suffers frequent blooms of cyanobacteria. In 2004, a bloom contaminated the primary drinking water source for Kisumu City, Kenya, stopping the supply of drinking water for almost 500,000 people. Algal blooms and oxygen depletion have been blamed for massive fish kills.

Marmara Sea, Turkey marine mucilage

Algae rapidly reproducing in nutrient-rich water created a thick layer of so-called marine mucilage clogging Turkey’s Marmara Sea. This “sea snot” has spread to nearly all of Marmara, an inland sea near Istanbul that connects the Black Sea to the Aegean. According to one hydrobiologist, “Marmara is now a sea just in name… If authorities act decisively, though, we can still save the Black Sea and the Aegean.”

Lake Okeechobee, U.S. algae blooms

Florida’s Lake Okeechobee has seen its algae bloom issues increase steadily over the last 50 years. The largest freshwater lake in Florida, Lake Okeechobee saw two-thirds of its surface (or 500 square miles) covered in blue-green algae in June of 2021. The concern now is not just for the lake, but for all its connected rivers, as water could be released from the lake in order to keep its water level down during hurricane season – a step that could mean spreading an active bloom to coastal areas.