Chesapeake Bay Coastal Bays Rivers and Streams Watersheds
Maryland Department of Natural Resources

Frequently Asked Questions

Microcystis aeruginosa is a naturally occurring algae in the tidal fresh and low salinity areas of Maryland's Chesapeake and Coastal Bays.  Large blooms of this algae occasionally occur during the warmest months of the year and can be quite striking in appearance.  Below are answers to some frequently asked questions regarding this organism.

What is Microcystis?

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Microcystis aeruginosa is a type of blue-green algae (also referred to as cyanobacteria). This species is colonial, which means that single cells can join together in groups as colonies a photo of microcystis in the Sassafras River, September 2000which tend to float near the water surface.  Colony sizes will vary from a few to hundreds of cells. It is a common bloom-forming algae found primarily in nutrient enriched resh waters and lower salinity estuaries.  Microcystis aeruginosa is one of more than 700 species of algae that may be found in water samples collected from the Chesapeake Bay and usually blooms in mid to late summer in this area.

What does it look like?
becomes very noticeable during bloom events.  Thick mats of the algae can coat the water so heavily that you cannot see your hand an inch below the surface.  In calm freshwater areas, it may look like someone has spilled green paint on the surface.  On closer inspection, the mats can be seen to be comprised of small flakes or balls.  If the algae is blown by wind or pushed by currents into higher salinity waters where it cannot survive, it generally takes on a greenish-yellow color and a chunky appearance as it dies.  See what the cells look like, visit our bay life guide.

What are we seeing on the Bay now?
another photo taken of microcystis on the Sassafras River in September 2000The Maryland Department of Natural Resources continues to conduct routine and response monitoring in the Chesapeake Bay and its tributaries. A boat survey of the Severn River on August 26, 2003 found no evidence of blue-green algal blooms. Between August 13th and 19th the most significant bloom conditions were observed on 1) the Sassafras River and its tributaries, 2) Lauderick Creek on the Bush River and 3) the Magothy River at Stonington. Toxin test results are pending for water samples collected from all three systems and sent to outside laboratories. Microcystin toxin has been identified from water samples collected on July 22nd from the Sassafras River and July 28th from the Bush River. Betterton Beach (Sassafras River, Kent County) remains the only beach closed due to persistent bloom concentrations of blue-green algae, presence of microcystin toxins and reports in July of swimmers experiencing skin irritation at this location. As in previous press releases, people and animals should avoid contact with water or drinking water containing high concentrations (a bloom) of this algae.

When and Where has it bloomed in the past?
Annual late summer blooms of Microcystis are frequently observed in the tidal freshwater portions of the Potomac River.  During the 1970's and early 1980's, this area of the Potomac experienced large blooms.  Since the early 1980's blooms have occurred to varying degrees in both the Potomac and Upper Bay.  Larger than normal blooms occurred in the upper Chesapeake Bay and it's tributaries during August and September 2000.  These 2000 blooms were probably the result of greater than normal amounts of freshwater and nutrients entering the Bay in 2000.

What causes it to bloom?
blooms are most frequently associated with warm, fresh, nutrient enriched water.  Blooms generally occur in mid to late summer and can carry on into the fall.  Excess nutrients (particularly phosphate) that are added to the Bay by human activities may contribute to the frequency and intensity of blooms. In particular, years with wet springs can wash greater than average amounts of nutrients into the Bay and its tributaries that can further fuel a bloom.

Does it pose a threat to animals or people?
a photo of what microcystis looks like in the bayAny large algal bloom has the potential to result in fish and shellfish kills by depleting the water of oxygen.  Algae can remove oxygen through normal respiration at night or through the decomposition process as the bloom dies.  In such situations, there may not be enough oxygen remaining in the water to support fish or shellfish in the vicinity.  Furthermore, as these large blooms die and sink to the bottom, they commonly release chemicals that can produce a foul odor and musty taste.

Some strains of Microcystis may produce toxins that have been reported to result in health problems to animals that drink the water, and minor skin irritation and gastrointestinal discomfort in humans that come in contact with toxic blooms.  Samples collected in the Sassafras River during 2000 also tested positive for the presence of toxins.

What is the State doing to monitor the situation?
Maryland Department of Natural Resources has maintained a Chesapeake Bay Monitoring Program that examines algae density and distribution throughout the year in the mainstem of the Bay, its tributaries and embayments since 1985.  Data collected as part of this program as well as additional data being collected in direct response to this bloom will be used to track the extent and duration of the bloom.  This information will be analyzed with water quality data (nutrient concentrations, salinity, temperature, etc.) collected baywide to better understand the environmental factors that have contributed to this bloom and insure that appropriate management actions are being taken to reduce the severity of future blooms.

What should I do if I see a bloom or have more questions?

  • The State operates a 24-hour Hotline at (888) 584-3110, in order to receive reports from the public regarding algal blooms, fish kills, and sick fish. The public and physicians are also asked to call this number in the event of human illness believed to be associated with algal blooms and fish kills.
  • For more questions on Microcystis Maryland Department of Natural Resources Tidewater Ecosystem Assessment Division: (410) 260-8630 (normal business hours).
  • Questions regarding human health impacts of Microcystis please contact your physician or your local health department.
  • Questions regarding animal (livestock) health impacts of Microcystis Maryland Department of Agriculture: (410) 841-5882 (normal business hours)

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