Swimming sicknesses: how warming waters can impact the safety of aquatic recreation

Originally a necessary life skill, swimming has evolved from basic protection against drowning to an enjoyable activity for many, and has become the fourth most popular recreational activity in the country. About 50 million Americans are swimmers taking to the many rivers, lakes, and oceans around the United States. 

Aquatic ecosystems provide many benefits to humans, including a myriad of recreational activities, which have become a big part of the economy. However, the availability and quality of these activities is being threatened by climate change, which is beginning to have a negative impact on human health. The warming waters increase the presence of photosynthetic organisms and the geographic range of microbes, and direct contact with contaminated water can spread diseases such as Vibriosis through pathogens and toxins. The contamination of our waters through harmful toxins leaves the future of many aquatic recreational activities hanging in the balance.

“What we see with climate change is that its principal mechanism is to redistribute existing pathogens into new areas,” said Dr. George Luber, the Adjunct Professor at the Center for the Study of Human Health at Emory University. “We’re identifying cases, and there definitely is a trend that we are seeing more of them in areas we didn’t expect to see before.”

Furthermore, aquatic recreational and tourist activities are also impacted by climate change in many other ways. As sea levels rise, processes such as coastal erosion, coral bleaching, and acidification occur, resulting in an increase in pollutants and contaminants. Warming temperatures amplify the effects, increasing the likelihood and spread of disease. 

“We live in a world where a lot of dominoes come into play anytime we have an issue,” said Dr. Geoffrey Scott, the Chair and Clinical Professor of the Environmental Health Sciences Arnold School of Public Health at the University of South Carolina. “Climate change by itself is a major issue, but when you put it in the context of all these other variables it’s like adding fuel to a fire.”

A study by the University of Arizona predicts the average annual global temperature to increase by 5-10 degrees in the next 50 years, with the Arctic warming at double that rate. This increase in temperature is caused by an increase in pollution and carbon dioxide emissions, leading to increased greenhouse gas concentrations, which trap energy from the sun that the ocean then absorbs. 

The number of waterborne illness cases is likely to continue to increase as well, as the spread of disease reflects the increase in temperature. 

“We’re seeing cases increase probably because of the amount of time that recreational activity is suitable. Because it’s warmer earlier, more people are in these colder water lakes that are now a bit warmer,” Luber said. “The warm southern lakes are typically where you would find [these cases], but now we’re starting to see it in much more northerly lakes.”

Many pathogens grow in aquatic ecosystems such as Vibrio, a family of bacteria containing about a dozen species that naturally live in coastal waters. Vibrio species are typically more prevalent in warmer waters, and climate change factors create more favorable growing conditions for such naturally occurring pathogens. 

“Warmer temperatures are conducive to pathogen growth,” Luber said. “Increased temperature increases the sustainability of the microbes that live there.”

Vibrio growth rates increase due to rising temperatures and contamination from pollution running into large bodies of water, and the combination of those conditions is conducive to the development of more harmful bacterias. As numbers grow with rising temperatures and pollution run-off, the organisms can get out of control and begin to affect human health. 

“The Vibrio bacteria are probably one of the best indicators of climate change effects,” Scott said. “We’ve gone from 8,000 cases of Vibrio bacterial illnesses in the U.S. in 2004 to over 80,000 cases today—and all of that is because of climate change.”

Vibriosis, an intestinal disease caused by Vibrio, can also lead to ear, eye, or wound infections, diarrheal illnesses, and in some cases, death. The bacteria typically enter the body through ingestion or open wounds in recreational waters.

“Wound infections can become systemic,” Scott warned. “You may be dead in three days if you are obese and have an underlying liver illness. A third of Americans are obese and may be potentially susceptible to this vulnerability.”

According to the Centers for Disease Control and Prevention, waterborne diseases affect over 7 million people in the United States each year. From 1996 to 2010, Vibrio infections tripled, tracking closely with rising ocean temperatures. As waters warm, Vibrio’s geographic range expands, appearing earlier in the season and in new areas farther north.

Previously colder regions are now experiencing waterborne illnesses as their climates become more hospitable to pathogens. Recreational areas that were once out of range for Vibrio are now increasingly at risk.

“What used to be an organism that caused illness in the Gulf of Mexico now causes illness in the Gulf of Alaska. The temperatures have warmed to the conditions where this illness will be manifest,” Scott said.

“Half of the world’s population lives in a coastal zone,” he continued. “That’s less than 17% of the planet’s land area, so [those] regions are extremely crowded and more vulnerable to water and air pollution along with the effects of climate change.”

The risks to aquatic recreation will continue to grow unless steps are taken. While large-scale efforts like restoring floodplains, preserving barrier islands, and protecting coral reefs are essential, individual actions matter too. Reducing personal carbon footprints and preventing pollution can help reduce the harmful effects of climate change and curb the rise of waterborne diseases.

“We need to increase our environmental quotient, not [just] our intelligence quotient,” Scott said. “If we increase our EQ, we will therefore raise our IQ and better understand the world around us.”