Algal blooms are underway in several Maryland rivers, the Maryland Department of the Environment (MDE) tells Bay Bulletin.
People started reporting cloudy, streaky-looking water in December, and since then, MDE says there are currently blooms in the lower Patapsco, Magothy, Severn and South rivers. Arundel Rivers Federation, the riverkeepers’ organization for southern Anne Arundel County, also reports blooms in the West and Rhode rivers and Herring Bay.
MDE spokesman Jay Apperson says the department took samples from the Magothy River and found high levels of the dinoflagellate algae Prorocentrum minimum. The algae isn’t toxic, but is the source of the “mahogany tides” seen in tributaries, usually in warmer weather.
“Blooms of Prorocentrum minimum in the fall and early winter are not unheard of – one persisted all winter last year in the coastal bays near Ocean City – but they are more common in the spring,” Apperson explains.
For their part, the Magothy River Association (MRA) says it has never seen a mahogany tide to this extent before, writing in a Facebook post, “This is not normal or close to normal.”
MRA points to nutrient pollution as the culprit on the Magothy:
“We have way too many nutrients getting into our rivers and feeding the Algae!” the group writes in a Facebook post, stemming from stormwater and septic system effluent.
MRA shared drone video of Cattail Creek near Asbury Road, showing the large swath of algae bloom. Watch below:
MDE says nutrients, salinity, and water temperature are all in the right range in the mid-Bay to support an algal bloom.
But, as Magothy River Association Vice President Sally Hornor points out, the fact that the bloom is occurring in winter may lessen its negative impacts:
“This phytoplankton is not a cold water organism so my best guess is that it will die off when the water chills down to its normal winter temps,” she explains.
When it dies off, its decomposition will be slowed by the cold. That means, Hornor says, “oxygen concentrations in the deep water may not be as critical as they would be in the summer.” She predicts the bloom won’t affect bottom-dwelling critters or underwater grasses, which aren’t growing now.
–Meg Walburn Viviano