Last winter's warmth and this summer's heat have likely brought on the early red tides, dense blooms of tiny marine plants called algae that contain reddish pigment and which happen in the lower bay every summer, researchers at the College of William and Mary reported.
A bloom in significant numbers can generate toxic byproducts harmful to both marine organisms and human health, they said.
However, there is currently no evidence of harm from the recent blooms, scientists at the Virginia Institute of Marine Science at William and Mary said.
The bay blooms are caused by Cochlodinium polykrikoides, a single-celled marine dinoflagellate.
"Blooms of this and closely related species may harm oyster larvae and other marine life, and are associated with fish kills and economic loss in Japan and Korea, but we've had no reports of any of these effects in local waters this year," researcher Kim Reece said.
Algae respond to the same conditions that encourage plant growth on land, researchers said, so excess nutrients from farms and yards, sewage treatment plants, and the burning of fossil fuels are one of the biggest challenges facing the Bay.
"There are three main ingredients for an algal bloom," Reece said. "Warm waters that favor rapid growth of algal cells, abundant nutrients to fertilize that growth, and wind and tidal-driven currents to confine the cells into a dense aggregation.
"Our recent heat and rains provide ideal conditions for bloom formation, so we'll continue to monitor whether the ongoing blooms become a cause for any concern."