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If Maryland experiences heavy snowfall this winter, biologists predict the Chesapeake Bay could end up with above-average levels of bacteria and toxic algae blooms next summer.

While human pollution can cause bacteria growth and algae blooms, natural factors, such as climate conditions, dictate their frequency. The amount of snowfall each winter is linked to algae bloom instances in the summer, since spring snow melt causes runoff, causing more nutrients to enter the bay.

“Some relation does exist between higher harmful ... blooms and increased runoff related to the amount of snow, rather than just winter temperatures,” University of Maryland Atmospheric and Oceanic Science Professor Raghu Murtugudde said. Maryland is expected to experience warmer than normal temperatures this winter, but also significant snowfall, so “harmful algal blooms may well turn out to be above normal next summer.”

Water temperature, the bay’s salt content and nutrient levels determine bacterial growth.

“Warmer temperatures mean more growth,” Maryland Department of Health and Mental Hygiene’s Environmental Health Bureau Director Clifford Mitchell said. The summer is generally the most high-risk time of the year for contamination.

Potential for infection and toxic exposure generally is not worrisome, although Maryland residents could benefit from avoiding recreational activity in the bay during certain high-risk periods when bacteria and algae blooms are high in frequency and toxicity, Mitchell said.

In certain situations, however, the state health department issues swimming warnings because of higher risks of bacterial infections. Heavy downpours lead to increased sewage run off, which potentially could contain strains of E. coli or promote toxic algae blooms, Mitchell said.

Although “a little consumption of bay water isn’t worrisome … we do worry about infections that come from exposure,” Mitchell said.

There’s a chance of exposure to bacteria and toxins for people who do recreational activity in the bay with open wounds, especially for those with compromised immune systems.

Even people “who are otherwise healthy but get puncture wounds from contaminated crab or shellfish” can develop infections, though only a few cases a year develop into significant or serious infections, Mitchell said. Raw seafood consumers also are at a small risk of exposure.

“Although not common, we have had cases across the country where blooms contain relatively high concentrations of toxins,” Mitchell said.

As for bacteria that grow naturally in the bay, Vibrio parahaemolyticus is the Maryland Department of Health’s main concern. But of all the people who swim in the bay each year, only about 30 to 50 individuals develop cases of Vibrio, which in its mildest form causes skin infections and stomach ailments although can lead to serious health problems if untreated or for people with compromised immune systems.

Melanie Gardiner, director of preparedness and response for the St. Mary’s health department, said there have been eight known cases of people contracting Vibrio during the past eight years in St. Mary’s County.

“Our incidents are low,” she said.

From the health department’s perspective, education is key to prevention, Gardiner said. If a wound becomes infected after exposure to water while fishing or swimming, a person should have it checked out by a doctor.

The Department of Health doesn’t directly monitor individual bacterial levels in the bay but looks out for warning signs such as algae blooms.

The St. Mary’s health department can post advisories when bacteria levels at 11 recreational bathing sites become too high, Daryl Calvano, the director of environmental health, said.

“The last few years have been very calm in terms of advisories,” he said.

Blooms occur when algae encounters its optimum growth factors, and natural predators like viruses and grazers don’t exist in high enough levels to suppress growth, said Allen Place, marine biologist at the Institute of Marine and Environmental Technology.

Blooms are fed by nutrients, mostly from human sources. Human waste and agricultural production are two of the main culprits of creating nutrient pollution, Place said.

“In the Chesapeake Bay, we are fortunate that most algae blooms have very little direct effects on human health,” Place said, citing possible skin irritation as one of the worst consequences.

The bay’s freshwater lakes and upper parts of the tributaries sometimes have Cyanobacteria blooms; however, that produce toxins that damage liver cells, which can cause cancer in humans and death for dogs when ingested, he said. To be safe, Mitchell said the public is advised to avoid the bay and its tributaries’ affected regions until any bloom clears.

Maryland isn’t alone in this phenomenon, Place said.

“General trend worldwide is greater frequency of algal blooms with longer duration,” he said.

Staff writer Jesse Yeatman contributed to this report.