September 4, 2003
Middle Potomac River conditions ripe with blue-green algal bloom.

Virginia citizens Connie and Nourmand Goulet photographed some of the thickest blue-green algal bloom water observed on the Chesapeake Bay this year in an area north of Aquia Creek on the Potomac River while boating during the Labor Day holiday weekend. (Figures 1 & 2).

A photo of what looks like mud in the prop wash is actually the thick blue-green algal bloom waters of the Potomac River upstream of Aquia Creek, VA, during the Labor Day weekend.
Figure 1. What looks like mud in the prop wash is actually the thick blue-green algal bloom waters of the Potomac River upstream of Aquia Creek, VA, during the Labor Day weekend. MD DNR sampled the area on September 2nd and identified bloom concentrations of blue-green algae at > 2 million cells/ml. Photo by Connie Goulet.
A photo of the appearance of green paint in the prop wash again illustrates the intense surface density of this bloom of blue-green algae on the Potomac River.
Figure 2. The appearance of green paint in the prop wash again illustrates the intense surface density of this bloom of blue-green algae on the Potomac River north of Aquia Creek during the Labor Day holiday weekend, 2003. Photo by Connie Goulet.

Maryland Department of Natural Resources sampled the river during routine monitoring on Tuesday, September 2nd. A sample from the Smith Point, MD station (closest to the area photographed by the Goulet's) contained one of the greatest concentrations of blue-green algae observed in the sampling program history at > 2 million cells/ml dominated by Microcystis aeruginosa. Samples throughout the rest of the region indicate the Smith Point, MD area as the bloom epicenter with lower concentrations of algae upstream to Indianhead and downstream to the Route 301 bridge at Morgantown (Figure 3). Bloom samples containing over 10,000 cells/ml of Microcystis occurred at most stations with Anabaena and Aphanizomenon also present between Maryland Point and Indianhead (Figure 4).

A photo from a bridge-view of blue-green algal scum accumulating along the shoreline of the Potomac River, Route 301 bridge at Morgantown, MD.
Figure 3. A bridge-view of blue-green algal scum accumulating along the shoreline of the Potomac River, Route 301 bridge at Morgantown, MD. Photo by MD DNR’s Laura Fabian, September 2, 2003.
Map of the Lower Potomac River showing the epicenter of the bloom at Smith Point and it's spread to other areas.
Figure 4. Map of the lower Potomac River sampling locations related to the recent blue-green algal bloom waters.

Monitoring surveys are extensive in their coverage of the tidal waters of our Bays. Aerial surveys further enhance our ability to observe the health of the Bay. However, the coverage is not exhaustive of all Bay waters. Pockets of blue-green algal blooms may be encountered during boating and other recreational activities. Cases of human illness this year have included itching, rashes and stomach discomfort from contact with or ingestion of bloom waters. People should take common precautions to reduce the risk of illness or discomfort related to blue-green algal blooms:

  • The public should not swim in areas where 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.

The Maryland Department of Natural Resources will continue to monitor all Microcystis 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.