In a recent review of historical data, Maryland Department of Natural Resources Walt Butler uncovered findings on possibly toxic plankton species in the Coastal Bays dating back to 1983. Intensive phytoplankton surveys of the St. Martin River were conducted in 1983 and 1992 by the Maryland Department of the Environment while evaluating impacts and upgrades to wastewater and industrial discharges in this watershed. Based on notes, drawings and preliminary identifications made at the time, Walt has discovered that Chattonella verruculosa, C. subsalsa and Fibrocapsa japonica were present in what appears to be lower concentrations ten to twenty years ago than what has been observed in recent survey years.

Chattonella and Fibrocapsa belong to a group of plankton known as the Raphidophytes. About a dozen species have been classified in this group worldwide and at least half are known to produce toxins or show toxic effects on living resources. In 2002, in addition to the Chattonella and Fibrocapsa species being found in the Coastal Bays, another potentially toxic raphidophyte known as Heterosigma akashiwo was also recorded in the region. No evidence of toxicity by any of these species has been correlated with fish kill events in Maryland waters.