The U.S. Food and Drug Administration identified the algal-produced toxin okadaic acid in low concentrations through testing of algae samples collected on 2/26/02 from the Potomac River by the Maryland Department of the Environment (MDE). Algae samples were processed by Maryland Department of Natural Resources for species identification and contained the dinoflagellate Dinophysis accuminata which has been known to produce okadaic acid in other areas of the world. Dinophysis concentrations declined at most sites compared to the previous week but higher levels were found in parts of Virginia so it is uncertain whether the lower levels represent a trend. Okadaic acid can be concentrated in shellfish and consumers of the contaminated shellfish may experience Diarrhetic Shellfish Poisoning (DSP). DSP can result in diarrhea, nausea and vomiting but has never been shown to be fatal; this syndrome has also never been reported for U. S. waters. Oyster tissues are currently undergoing testing for the presence of toxin. The MDE and Virginia authorities will keep the current temporary closure until there is sufficient evidence that shellfish consumption does not pose a health risk. Algal monitoring will be repeated this week.