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Algae naturally occur in the water in southeast North Carolina and are usually harmless. In fact, said Dr. Amy Mead, New Hanover County NC Cooperative Extension director, algae are often helpful because “these simple plants form the basis of our food webs.” Mead said, “Algal overgrowth is very common in our ponds due to the favorable conditions created by heat, light, and nutrients.” However, standing and slow-moving water like that found in ponds and creeks can sometimes breed a certain type of blue-green algae called cyanobacteria that can be harmful to humans, pets, and fish.
Mead said, “The trend in our climate towards hotter summers and more intense, concentrated bursts of rainfall does create ideal conditions for these blooms to occur.”
She added that cyanobacteria are “heat-lovers” and thrive in high-temperature water. That makes stormwater retention ponds and other shallow pockets of water the perfect environment for them, especially where there is calm or stagnant water, plenty of sunshine, and – most of all – high levels of nutrient-rich runoff.
“Just like putting Miracle-Gro on your plants, these microscopic algae will respond to high levels of nitrogen and phosphorus with rapid growth. Blooms here in the Cape Fear River Basin can also be triggered after big storm events, as this flushes loads of nutrient-rich runoff from agricultural and urban areas into the system,” she said.
Dr. Michael Mallin, UNCW Research Professor of Marine Science, has been studying local waterways for decades. Along with his UNCW colleague Dr. Colleen Brown, he has “detected an increasing trend in nitrogen and phosphorus, and fecal coliform bacteria in numerous long-term stations in the Lower Cape Fear, particularly in the Black and the Northeast Cape Fear subbasins.” This fecal matter is draining into our water from upriver swine and poultry CAFOs (Concentrated Animal Feeding Operations), which are much less regulated than water treatment plants.
Large water treatment facilities are tested regularly for nitrogen and phosphorous, the nutrients that feed algae, and the state’s Department of Environmental Quality can make them correct any issues. CAFOs on the other hand, “They don’t have to sample the water that runs off into those branches. They are inspected once a year by somebody from DEQ. But that means that, during the year when it rains or floods, nobody’s sampling those streams,” according to Mallin.
Since they aren’t being tested, they also aren’t being made to correct the resulting issues in the water.
CAFOs store their wastewater in lagoons. During flooding from storms, these lagoons can run over into creeks and rivers untreated. A 2022 study showed an 11% increase in ER visits for gastrointestinal illnesses after hurricanes Matthew and Florence, likely related to these lagoons flooding into the drinking water. In addition, Mallin said, “Major agriculture, including livestock production, have very powerful, well-paid lobbyists, and they pressure the [NC] general assembly members saying that it’s going to be too expensive for them to control the runoff coming from the waste, so instead they’re allowed to just pour their waste into a lagoon and hope that it gets partially treated. Then they spray some of it out on the fields.” This runoff and sprayed fecal matter makes its way down through the soil and into the water table, where they move laterally to the nearest water body and eventually becomes food for algae overgrowth. Mallin said, “Climate models [show] general consensus that hurricanes are going to be stronger. That has obvious implications of more runoff, more flooding.”
Mead said, “[S]tormwater runoff may be high in nutrients and other contaminants such as fecal bacteria from pet waste. High nutrients from that runoff, combined with clear, shallow, hot water can create the perfect conditions for algal overgrowth. We can also see potential for HABs [Harmful Algal Blooms] in slow-moving, shallow creeks and lakes as well.”
Mallin said that people can help control runoff that feeds algae by cleaning up pet waste, primarily dog feces, and avoiding too much fertilizer on ornamental gardens and lawns, since these are the largest contributors to issues in urban areas like Greenfield Lake. Greenfield Lake is on the DEQ’s 303D list, a list of waterways in North Carolina to avoid because of high chlorophyll, an indicator of algae overgrowth.
Mallin added that one contributing factor not related to human activity is visiting wild birds, including cormorants and Canada geese. These birds contribute to the phosphorous with their droppings, which eventually feeds more algae blooms.
Dangers of cyanobacteria
Some infected water may be blue-green, but some shows no signs at all. Cyanobacteria are dangerous to dogs and children who play in or drink contaminated water. Mead said that some dogs in North Carolina have become sick or died “after swimming in ponds due to toxic algal blooms. Dogs in particular tend to drink a lot of pond water while playing and then also groom themselves after leaving the water, potentially ingesting the toxic cyanobacteria. In addition, toxicity is relative to body mass and dogs' smaller sizes mean that a smaller dose may be more likely to cause a life-threatening reaction. This is true for children’s smaller bodies as well, although children are less likely to gulp down pond water. The best practice is to keep dogs and children out of ponds.”
In August 2019, the Charlotte Observer reported that three dogs died in Wilmington shortly after swimming and wading in a local pond and being exposed to cyanobacteria. Another died in Georgia, and three more in Texas around the same time. A toxin produced by the algae can affect an animal’s liver and nervous system. Although healthy humans are unlikely to die from cyanobacteria, the CDC says it can cause skin and respiratory irritation, gastrointestinal issues, and neurological and organ damage.
Algal blooms can also cause trouble for animals that live in the water. Algae can block sunlight or deplete the water of oxygen that fish need to breathe. Cyanobacteria can also poison fish, birds, and other aquatic animals directly. This can lead to fish kills, like a large one in September 2020 that killed 1,000 carp, according to the CDC.
Mallin said that cyanobacteria have “mechanisms that protect it from excessive sunlight… [photoprotective] pigments that protect it from strong UV. Otherwise, strong UV kills most bacteria.” Once cyanobacteria are established, blooms are likely to recur.
Recognizing a dangerous bloom
According to Mead, sometimes there can be dangerous conditions in ponds, even if there are little or no signs of algal blooms. And sometimes, discoloration isn’t a danger.
Mead explained, “Many of our cleanest and most beautiful rivers and streams have a brown or tea color to the water due to tannins leaching from organic material. Many times in the spring, we get calls about a yellow, scummy look to the water and it is actually pollen on the surface of the water. And of course, there are many, many species of algae that can grow in ponds, lakes, and streams that are completely harmless and non-toxic.”
Mead suggests following NCDEQ’s advice: “When in doubt, stay out. It's best to stay out of water bodies such as retention ponds, golf course ponds, and shallow creeks. In particular, residents should keep out of water that appears bright green or blueish, or scummy. Sometimes these cyanobacteria blooms are described as looking like spilled green paint or pea soup.”
Mallin said, “If you see surface scum that covers a large area of the lake, that’s not good. That means that it’s a bloom of some sort of algae. It may be blue-green or it could be just green algae, but it’s an overgrowth. It shouldn’t be like that…If the water looks like it’s very green throughout, that’s probably an unhealthy algal bloom as well.” In addition, Mallin said, “Some pond water looks yellow-green, but that’s actually more blue-green algae (cyanobacteria).”
Sometimes these blooms can have an unpleasant “very powerful” smell, but, “not always...Sometimes there’s no smell,” he said.
Water quality
Mallin said he wished more elected officials in North Carolina would pay attention to water and air quality.
“Oftentimes, they fall prey to powerful lobbyists who represent polluters. Pollution can be cleaned up at the source, which takes political willpower to do so. There are some really good politicians who understand, but there’s too few,” he said.
Mallin said officials need to be aware of the problems surrounding cyanobacteria and other dangerous algae blooms as they become more prevalent with hotter and longer summers in our area. He suggested that scientists and elected officials can work together on environmental issues, adding that there’s an economic incentive: tourists’ dollars.
“Clean water helps tourism,” he said.
Mallin said he worries that, “It’s only going to get worse as long as you have people in the general assembly who put the environment [and people] last and development and polluters first.” He suggested the most important change to Coastal North Carolina policy to improve water quality would be “stricter development regulations that increase buffer zones and decrease impervious surfaces.” He argued that buffer zones allow more undeveloped land between development and nature. In the Cape Fear region, this would mean less development close to the river, and keeping trees and other natural landscape to clean runoff, prevents soil erosion, and protect from flooding. Mallin also suggested that less paved land allows water to flow naturally into the soil, which can filter it before it reaches drinking water, as well as preventing flooding and refilling groundwater aquifers.
Mead said it's worth remembering that most of us love to be near, on, and in the water; that’s why we live here.
“We just need to be knowledgeable and aware that our unique climate and geography, characterized by slow-moving, shallow water, combined with our rapid coastal development, can create conditions in which these blooms occur,” she said
To see if there are reported local algae blooms check out the algae bloom website. To report dead fish or suspected algae, contact the nearest DEQ regional office or submit a report online so NCDEQ can investigate and run samples to check for safety.
