When the famous Lincoln Memorial Reflecting Pool in Washington, D.C., suddenly turned bright green, many people were surprised.
The unusual color quickly became national news. The cause was a large bloom of cyanobacteria, often called blue-green algae. Although they look like algae, they are actually a type of bacteria.
Some kinds can produce dangerous toxins that can harm people, pets, and wildlife.
According to environmental engineer Steven Chapra from Tufts University, the bloom was not unexpected.
He explained that cyanobacteria grow quickly when three things come together: plenty of nutrients, lots of sunlight, and warm water.
The Reflecting Pool has all three. It is shallow, the water moves very little, it receives full sunlight all day, and it is filled with water from the Potomac River that contains nutrients such as nitrogen and phosphorus.
A dark-blue pool bottom also absorbs heat, making the water even warmer and helping the bacteria grow faster.
Chapra believes the problem could be solved without major cost. Better water circulation and filtration could reduce the nutrients that feed the bacteria.
Repainting the pool with a lighter-colored surface could also help keep the water cooler, making blooms less likely.
While the green pool caught public attention, Chapra says it highlights a much bigger problem. Harmful algal blooms are becoming more common in lakes and reservoirs across the United States.
His research suggests that climate change could increase the number of harmful blooms to two to five times today’s levels, with some of the biggest increases expected in the northeastern United States.
Warmer temperatures give cyanobacteria an advantage over many other tiny water organisms. They grow well in warm water, can float on the surface to capture more sunlight, and are not a favorite food for many small aquatic animals.
As winters become shorter and lakes stay ice-free for longer, the growing season for these blooms also becomes much longer.
Not every bloom is toxic, but many can release chemicals that damage the liver or nervous system. People may be exposed by drinking contaminated water or by coming into contact with affected lakes and ponds. Dogs are especially at risk because they often drink water while swimming or playing.
These blooms also affect drinking water. In 2014, nearly 500,000 people in Toledo, Ohio, were told not to drink tap water after toxins from a bloom contaminated the city’s water supply. Water treatment plants can remove many toxins, but doing so is expensive and sometimes difficult.
Everyone can help reduce the risk. Using less fertilizer, cleaning up pet waste, and planting native plants or rain gardens can reduce the amount of nutrients washing into waterways.
If you see water that is bright green, covered with thick scum, or has a bad smell, stay out of it and keep children and pets away. Reporting blooms to local authorities can also help protect the community.
The green Reflecting Pool may look like a local problem, but it serves as an important reminder that protecting clean water will become an even greater challenge as the climate continues to warm.
