Can oysters make you sick? Because oysters filter their food from the water in which they live, if that water becomes contaminated they can concentrate harmful toxins in their meat. One of the most dangerous is paralytic shellfish poisoning (PSP). To protect public health, the Washington Department of Health monitors PSP in shellfish from hundreds of sites in Puget Sound and the coastal estuaries the year around. You can check the Biotoxin Bulletin for up-to-date information on harvest area closures, or call 1-800-562-5632. PSP is a biotoxin produced by the naturally-occurring dinoflagellate Alexandrium catenella. When consumed via contaminated shellfish, the biotoxin can produce symptoms within an hour or two, ranging from tingling or numbness of the lips to speech impairment and interference with breathing and moving. There is no known antidote and death may occur in some extreme cases. Alexandrium catenellamay be present in very small numbers all year long. However, in spring when the water warms, nutrients are abundant and the length of daylight increases, many forms of phytoplankton, including Alexandrium, bloom until they are so numerous that they color the water green, yellow or brown. Shellfish may become highly toxic from PSP at numbers far lower than needed to produce visible blooms. PSP blooms usually continue until surface nutrients are exhausted and water temperatures drop. Over the decades, several areas in Puget Sound have been free of PSP, including Hood Canal and parts of south Puget Sound. When blooms occur, oyster harvest areas are closed until the water quality returns to normal. A bloom in the fall of 1998 resulted in an unprecedented closure of much of the south Puget Sound shellfish industry during the holiday season, the most critical commercial season of the year. (Adapted from an article by Tim Determan, Department of Health, Office of Shellfish Programs. Sound Waves, Spring 1998.) Return to News You Can Use