Lee Karrh of Maryland DNR reported rust-colored water on the Choptank River at the Route 50 bridge in Cambridge, MD on May 13th. Routine water quality monitoring sampling by Maryland Department of Natural Resources on Monday, May 19th, collected water from the region that contained significant concentrations of the Mahogany tide dinoflagellate at 44,750 cells/ml. Scientists with The Academy of Natural Sciences Estuarine Research Center visited the area on May 20th and also reported bloom concentrations of Prorocentrum minimum at 44,000 cells/ml.

Mahogany tide conditions can be expected to remain in the area for at least the next week. Significant rains over the upcoming weekend may bring enough freshwater downriver to begin moving the bloom further downstream out of the Cambridge area as we move into June. Also, Prorocentrum minimum typically declines as summer conditions arrive, however, with cool spring conditions the blooms have persisted in some areas for more than two weeks now. During 2000, turbid water conditions persisted for nearly 45 days on the Rhode River caused by the same type of Mahogany bloom.

To learn more about how the Bay monitoring data shows changes in important water quality parameters, please visit the Monitoring Stories and Highlights section of Eyes on the Bay.