August 20, 2004 Microcystis, blue-green algae surface scums continue but intensity declines on the Potomac River.

Routine water quality monitoring by the Maryland Department of Natural Resources (DNR) and the Academy of Natural Sciences Estuarine Research Center (ANSERC) continued to detect blue-green algal bloom waters on the Potomac River August 9 and 10. Intensity and distribution have declined slightly for the region but there remains significant bloom waters evident largely in Charles County. The greatest abundance of the possibly toxic cyanobacteria (i.e., blue-green algae) Microcystis has moved downriver towards Smith Point; bloom concentrations of 105,000 cells/ml to 169,000 cells/ml were detected in the region during the latest monitoring effort. An additional sample collected during DNR routine monitoring on August 9 at Smith Point recorded 502,440 cells/ml (Figure 1).

Chlorophyll measures conducted by ANSERC showed elevated concentrations (835-2028 ug Chlorophyll a/L) from Quantico Creek to Smith Point in Charles County (Figure 1). These measures are indicative of abundant algae though not necessarily all from the Microcystis blooms which have a prevalence of other biological pigments not specifically detected by the monitoring technology available at this time.

Concentrations and distribution of cyanobacteria increased in the Potomac River since they were first observed during late spring on June 7. A Mattawoman Creek sample that day measured 34,450 cells per milliliter and Sandy Point (upstream of Mallows Bay) had 2.4 million cells per milliliter. In late June and early July high abundances led to beach closures by Virginia Department of Environmental Quality downstream of the Route 301 Bridge at Colonial Beach, VA. On July 3, the beach reopened with subsequent declines in Microcystis. However, Maryland DNR detected widespread presence of Microcystis on July 6 upstream of the Route 301 Bridge, the precursor to the extensive blooms observed in late July and continuing this month.

• The public should not swim in areas where a blue-green algae bloom is evident.



• Do not drink water from any area with the appearance of a blue-green algae bloom.



• If contact is made with problem water, simply wash off with fresh water.
  In some cases, skin irritations may occur after prolonged contact. If irritations persist, see a physician or local health care provider.



• Keep pets and livestock away from bloom areas.
  Blue-green algal blooms may contain toxins that could be harmful or fatal to pets and livestock.



• Do not eat viscera (internal organs) of fish caught in bluegreen bloom waters.



• Inhalation exposure to blue-green algal bloom waters may result in irritation of the eyes, ears, nose and throat with extended recreational activity on such waterways.

Please note that illness associated with harmful algal blooms is now a reportable illness so physicians should be reporting these to local health departments. The MD DNR in coordination and cooperation with DHMH and MDE will continue to monitor all blue-green algal blooms throughout the state. For up to date information on all of Maryland's harmful algal blooms and water quality, please visit Eyes on the Bay