Algal Blooms, Like the One in D.C.’s Reflecting Pool, Caused by Sunlight, Slow-Moving Water

As the nation watched spellbound the struggle to tame the algae bloom in Washington, D.C.’s Reflecting Pool this summer, similar blooms were happening in South Carolina and around the country.

These blooms can appear as thick, discolored, and foul-smelling scum on the surface of ponds, lakes and other bodies of water.

But besides their obvious aesthetic issues, they can be dangerous, leading to illness — sometimes serious — in people, pets, and other animals that come into contact with them.

Algae are small, microscopic plant-like aquatic organisms that play a critical role in the ecosystem, says Debabrata Sahoo, Ph.D., associate professor and Sustainable Water Resources Extension Specialist with Clemson University’s Department of Agricultural Sciences.

They are a vital food source for fish, he said, but under the right conditions, such as enough nutrients, warm temperatures, sunlight, and slow-moving water, they can proliferate.

When they do, it’s called an algal bloom, he said.

The Reflecting Pool presented the “perfect recipe” for algae growth, Sahoo said, because of its shallow, slow-moving water, combined with high temperatures and sunlight.

But while some blooms are limited to an unpleasant appearance, others can produce toxins that are harmful, either to the aquatic ecosystem, resulting in a fish kill from lower oxygen levels, for example, or to people and animals, he said.

“Certain harmful blooms, if they produce those toxins, the water body could be detrimental to humans recreating in the water, and detrimental to pets, livestock, and birds,” he said. “These toxins have the potential to cause headache, nausea … diarrhea, stomach pain, and long-term exposure can lead to liver and kidney damage and potentially lead to hospitalization.”

Common symptoms — caused by touching or swallowing water or food containing cyanobacteria, or blue-green algae — also include rash, coughing, watery eyes, nose irritation, and sore throat, according to the U.S. Centers for Disease Control and Prevention. Breathing in tiny water droplets can also cause symptoms, the agency reports.

The most serious symptoms, typically caused by eating seafood or swallowing water that contain these toxins, also include seizure and irregular heartbeat, CDC reports.

“Animals can get sick and die within hours of swallowing harmful algal bloom toxins in water, food, or algae,” according to the agency, which lists symptoms in pets, livestock, and wildlife as including vomiting, loss of energy, stumbling and falling, and seizures.

Algal blooms occur naturally in lakes, ponds and other bodies of water all over the country, according to the South Carolina Department of Environmental Services.

While harmful algal blooms, or HABs, can look like foam or thick layers of algae on the water, they may also appear as “bright green spilled paint or blue-green discoloration of the water,” DES reports. They can also cause the water to appear red, brown, or blue, according to the department, but they can't always be seen.

The agency monitors recreational waters for HABs and issues warnings to protect the public when one is identified. Earlier this year, HABs were reported at Lake Hartwell and Broadway Lake near Anderson, South Carolina, for example. 

And while warm weather and other conditions contribute to these blooms, humans also play a role, largely through agricultural and storm water runoff, and other sources, Sahoo said.

Fertilizer contains phosphorus and nitrogen, which feed the algae, he said

“Algae need food like that, and where is it coming from, the land or other point sources,” he said. “Applying fertilizers could make its way to water systems through runoff.”

Waste water treatment plants are another source of these nutrients, he said, noting that there is legacy phosphorus in these systems that, under certain conditions, can get back into the water column.

And while waterfowl can get sick and die from HABs, they can also be another source of them through their fecal matter, he said.

Climate change also contributes to algal blooms, Sahoo said, noting that warmer temperatures over longer periods of time can lead to extended seasons and accelerated potential for HABs.

“Think about what has happened in several years because of changes in weather patterns,” he said. “Intense storms and drought create conditions for algae to proliferate, and storms bring runoff to water bodies.”

So prevention by employing a multipronged approach is really the key to reducing HABs, Sahoo said.

“Reduce the amount of fertilizer that is used, apply buffers such as plants and trees that can take up those nutrients to help filter the water before it goes into the ecosystem — these are nature-based filtration techniques which will also reduce the amount of nutrients in sediment,” he said. “And don’t apply (fertilizer) right before a storm event.”

Newer technologies, including nanobubblers like those used in the Reflecting Pool, as well as ultrasonic algae control systems and chemical algaecides, can also reduce the blooms, he said.

Getting the water moving, as with nanobubblers, can help, he said.

“But are we going to use 100 in a lake, or 1,000?” he asks. “Because algae is critical. We don’t want to kill it. It provides food to fish and other aquatic life.”

That means careful adoption of scalable technologies, Sahoo said.

Meanwhile, AI-based technologies are being developed to alert and provide information to stakeholders that can help analyze data and shorten the detection time, he said.

“We need to spread the word that this is a problem we need to tackle,” he said. “We have done research, but more needs to be done in terms of technologies, and cheaper technologies.”

A summary report from the CDC looking at data from 2022 found that 15 states reported 372 HAB events that year that resulted in 95 human illnesses — 45 percent of which were among those younger than 18 — and more than 102,000 illnesses among animals.

Because pets can also be affected, Sahoo advises keeping an eye on the color of the water.

“And don’t let your dog recreate in the water until you test it,” he added.

HABs also have the potential to kill livestock who drink water from affected ponds, which can mean a financial loss, he said. So farmers should keep an eye out for blooms and use other sources of water for their livestock if they spot one, he said.

“Sometimes you will see a scum, a thick mat that has a bad smell, like rotten eggs,” he said. “When you have the potential for harmful bacteria, use other water supplies.”

Sahoo said some limited literature even suggests that irrigation water contaminated with harmful algal toxins could make its way into the agricultural food supply. But more research is needed, he said.

Clemson’s Extension Service has held several workshops to help farmers, he said, and has a website that provides them with information.

“It’s an evolving process,” he said. “And we have to engage farmers in the discussion.”

Clemson will test water samples sent in for the algae that produces toxins, but that can take a couple of days, Sahoo said. A quick test kit is available but only shows the presence or absence of toxins.

The DES says there’s “always a potential risk when swimming in natural water bodies” because they’re not sterile environments. And blooms can grow quickly and become an issue before the agency is aware of them.

As a result, it recommends that people evaluate the water before swimming or otherwise recreating in it and avoid it if it looks discolored, has a foul odor, or if there are dead fish or other animals in it.

A general rule of thumb with any natural water body, the agency says, is “When in doubt, stay out.”

“It can happen anywhere,” Sahoo says. “And the number of blooms has increased because of human and weather activities.”

For more information, go to Harmful Algal Blooms | South Carolina Department of Environmental Services.