Annapolis – May 26, 2020 (updated 5.29.20). That ugly red-brown water we’re witnessing in the Severn River right now is an algae bloom, the infamous Mahogany Tide.
The top picture at right is what the algae bloom did to the harbor in West Severna Park.
The picture below is what the harbor in West Severna Park looked like just a few days earlier when their community was celebrating their healthy looking water full of underwater grasses and the curious mating rituals of carp.
When these Mahogany Tides show up, they obscure everything. Clarity reading in this muck is just abysmal.
On Back Creek, which like all the creeks is experiencing this algae bloom, we found visibility limited to barely 12.5 cm (roughly 5 inches).
The red color is caused by an explosion of the algae known as Prorocentrum minimum.
Depending on the intensity of a bloom like the one we’re suffering through, these blooms can cause local fish kills, invertebrate kills and the loss of habitat.
This does not bode well for fishing because when the algae bloom completes its life cycle it will likely deplete oxygen and create a dead zone on the bottom of the River. This happened in 2019. We had a similar algae bloom and then a persistent and widespread dead zone. This causes fish to swim away to find cleaner water with more oxygen.
Note: This event is different from the red tides that plague the Gulf Coast of Florida. That one is far more intense and is harmful to humans and fish alike.
The Mahogany Tide we’re experience on the Severn is not normally toxic to humans, though Maryland’s Department of Natural Resources does report that there are rare cases where eating shellfish that have been contaminated with the algae can be harmful.
Click here for DNR details on Prorocentrum minimum.
The National Oceanic and Atmospheric Administration website also cautions that although human toxicity is rare, an intense algae bloom can sometimes be debilitating or even fatal.
— Mackenzie Miller