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August 9, 2004
Macroalgae common to Upper Western Shore tributaries and upper Chesapeake Bay this year.

On Saturday July 31, DNR staff’s Peter Tango spent an early morning trip on the upper Bay with watermen Steve Lay and Brian Bailey, and Mary Madison, editor of the Waterman's Gazette. There were reports this summer of a green slime covering crab pots within a couple of days of deployment. The slime was identified by DNR’s Walt Butler as a filamentous blue-green macroalgae Lyngbya latissima. The algae was so abundant in June and July that crabbing efforts for most other watermen moved below Pooles Island to avoid the difficulties caused by algae fouling the crab pots (Figure 1).

Water clarity peaked for the year in the upper Bay during the period when the watermen indicated the macroalgae was most abundant in the region (June and July). Secchi depth, an index to water clarity, was above the Maryland water quality monitoring program long-term averages between 1985-2003 for those months and reached record clear water conditions in July of 1.9 m at the Turkey Point station. Investigations are continuing to look at possible linkages between the algae, water clarity and abundances of submerged aquatic vegetation being reported by citizens in the region since May.

Figure 1. 2004 Filamentous Algal Bloom Tracking


Pockets of blue-green algal blooms may be encountered during boating and other recreational activities. 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 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