In the course of 30 years, the Chesapeake Bay warmed up by about 2 degrees Fahrenheit.

That’s according to researchers at William & Mary’s Virginia Institute of Marine Science, who also found that the bay is warming about three to four times faster in the summer than the winter.

“The amount of warming that we see in the summer comes out to about just under one and a half degrees Fahrenheit over 30 years, which is quite rapid and concerning,” said Kyle Hinson, lead author of the study and a PhD student at the institute.

“We’re really concerned about this elevated summer warming because warmer waters can help expand and worsen the annually occurring dead zone that happens in the bay when oxygen levels are low,” he said.

Lower oxygen levels can impact crab habitat and fisheries that people depend on for their livelihoods.

“And warmer waters can cause harmful algal blooms, which can affect recreation, tourism or the safety of the waters that people use all around the bay,” he said. “It makes the job of improving the water quality that much harder with the work that’s being done to reduce nutrient runoff.”

So what can be done?

“There’s not a lot of mitigation that can be done, besides limiting greenhouse gas emissions, which would reduce future warming in the atmosphere, which is what’s ultimately driving most of these trends,” Hinson said. “But it will help managers plan for the effects of climate change on the bay and what they might need to account for.”

The study’s findings are based on data stored by the Chesapeake Bay Program, which is an office of the U.S. Environmental Protection Agency. The readings were collected by Virginia’s Department of Environmental Quality and Maryland’s Department of Natural Resources.

“They go up and down the bay’s Maryland portion and sample from top to bottom at all these stations along the central channel of the Chesapeake Bay, at least once a month. And they look at temperature, salinity, all kinds of important water quality aspects. And then Virginia does the same thing. And it’s not just in the main channel; it’s also in tributaries,” Hinson said.

The findings have been published in the Journal of the American Water Resources Association.