Green and yellow pollen slicks hit rivers and bay, sign of climate change

Green- and yellow-colored slicks made up of tiny grains of pollen are hitting local rivers and the Chesapeake Bay this spring, scientists said, and they’re a sign of climate change.

The Chesapeake Bay Foundation said area residents have contacted the organization recently about the pollen slicks, but experts said they’re not harmful to waterways - just difficult for humans who suffer from allergies.

Joe Wood, a scientist for the foundation, said data shows pollen levels are increasing and that’s associated with climate change.

"Once it gets warmer, we have a longer growing season and trees are active for longer, so that increases the pollen count,” he said. "That’s why we’re experiencing indexes of pollen that have been on the rise for the last 30 years.”

Pollen has been at peak levels at times this spring in the DC region as trees - mainly junipers, oaks, maples, birch and cedars - release the grains, experts said. Homes, sidewalks and vehicles can become coated with a greenish film when the wind blows. And when pollen lands on water, it can accumulate into a swirl atop the surface.

Pollen in the water in Annapolis in April 2024. Photo by Chesapeake Bay Foundation

For the first three weeks of February, tree pollen counts in the area were not as noticeable, according to Susan Kosisky, director of aerobiological reporting and evaluation at the US Army Centralized Allergen Extract Lab in Silver Spring, Maryland. But once warmer 60- and 70-degree temperatures "kicked in,” Kosisky said, "pent up pollen from flowering trees took flight.” March came in with what she calls a "pollen explosion” as more trees released pollen.

Typically, daily average counts of pollen in the second week of March in the DC region are roughly 183 grains per cubic meter, but this year they were much higher at 657 grains per cubic meter.

With rain and cooler weather for the start of April so far, Kosisky said, there will be some relief for those with pollen allergies. She said she’s expecting to see pollen counts more in the 300 per cubic meter range.

But the barrage isn’t over yet, she said. Certain treeshave "brown, wormy, stringy-looking things” - called catkins - that have "tiny, little flowers on them that release billions of pollen grains into the air,” Kosisky said, and "there’s still a lot of those hanging on oaks.” Oak pollen, she said, accounts for 47 percent of the area’s annual pollen load.

Kosisky’s philosophy: "As the weather goes, so does the pollen blow.”
Once people have been inhaling pollen over several weeks, Kosisky said, they typically can have a reaction to even lower amounts of pollen.

The Asthma and Allergy Foundation of America ranks the country’s top cities for allergies, including Richmond at No. 8, Virginia Beach at 11, Baltimore at 60 and Washington at 70. Wichita and New Orleans rank as Nos. 1 and 2, respectively. Roughly 25 percent of adults in the country have seasonal allergies, according to the US Centers for Disease Control and Prevention.

Wood, the foundation scientist, said that because pollen is a natural substance, it’s not toxic to animals or aquatic life. One tip for those who suffer from seasonal allergies, Kosisky said, is to be mindful that pets taken outside can get the pollen stuck in their fur.

"Then you’re wondering why you’re reacting to allergies,” she said. "It’s because the pollen’s in their coat.”