December 10 , 2004
Mahogany Tide evident in Anne Arundel and Baltimore County waters.

Maryland Department of the Natural Resources (DNR), Department of the Environment (MDE) and Morgan State University (MSU) sampled waters of the Patapsco River system on December 6 and 7, 2004, noting reddish-brown waters. The algal bloom waters are almost exclusively being produced by the Mahogany Tide dinoflagellate organism Prorocentrum minimum. A sample from Bullneck Creek off of Bear Creek in the Patapsco River contained 215,000 cells/ml Prorocentrum on December 6 while a sample near the Turner Station boat ramp on Bear Creek on December 7 by MSU contained an estimated 140,000 cells/ml and generated a bright orange wake behind the boat.

On December 9, Maryland Department of the Environment responded to a citizen call regarding water quality on the Magothy River, between Old Man and Cattail Creeks, along North Drive. This investigation revealed another Mahogany Tide bloom site with 262,300 cells/ml of Prorocentrum minimum.

Indications of autumn Prorocentrum blooms this year were first noted on November 15 on the Severn River by Maryland DNR with a sample from the long-term water quality monitoring station yielding relatively low level bloom of 13,303 cells/ml. On December 5, citizen Pierre Henkart noted reddish-brown waters on Saltworks Creek and provided a sample estimate of 220,000 cells/ml, most likely dominated by P. minimum.

While Prorocentrum frequently blooms in the spring, Mahogany Tide blooms have been observed in Maryland in all seasons.