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Skip Navigation LinksDNREC : Division of Water : Information : Other Information : Blue-Green Algae

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            Blue-Green Algae in Delaware

Blue-green algae – also known as cyanobacteria – are naturally occurring
Typical appearance of a highly-developed blue-green algal bloom in a Delaware pond. Photo by Robin Tylermicroscopic organisms that increase in density or “bloom” under certain
environmental conditions, most commonly an oversupply of nutrients combined
with warm water temperatures.

Blue-green algae blooms can form dense mats that appear most often as thick green, white or reddish-brown scum on the surface of the water. The blooms or dense mats can cover entire areas of a pond or only certain portions such as along the shoreline. When the algae blooms die and decay, the water can appear multi-colored and mistaken for a paint spill.

Blue-green algae blooms occur annually throughout Delaware on ponds and lakes of all sizes and some tidal freshwaters. They begin forming during summer and are often particularly vigorous in early autumn.

Certain strains of blue-green algae can produce toxins and the incidence of this occurrence is unpredictable. The best precaution is to avoid contact or exposure to water with blue-green algae blooms or scum and if contact is unavoidable or accidental, to wash thoroughly after contact. Recreational activities that may inadvertently result in swallowing or inhaling droplets of water from areas of scum should be avoided. To date, there have been no reported cases of human or animal illness in Delaware associated with exposure to blue-green algae..Sign for blue-green algae placed at select state ponds and lakes throughout Delaware

In 2009, a Water Advisory sign was developed by subject matter experts from DNREC, the Division of Public Health and the Department of Agriculture. These signs are posted at select ponds and lakes throughout Delaware alerting the public to the presence of blue-green algae and its possible harmful effects on people and animals.

Health effects to humans from skin contact can include rashes, hives and blisters, especially on lips and under swimsuits. Less frequent reactions reported nationally in individuals who have inhaled water containing high concentrations of blue-green algae toxin include runny eyes and nose, sore throat, asthma-like symptoms or allergic reactions from asthma. If swallowed, reactions could include diarrhea and vomiting, liver toxicity, kidney toxicity and neurotoxicity.

Pets may have the same adverse reactions as humans and should be washed or rinsed off after contact with the water. If scum-laden water is swallowed, call your veterinarian.

Toxins from blue-green algae have been documented in waters in other parts of the country where the algae is not visible or in full bloom. The problem is global as well as local and is being addressed in many other countries as scientific knowledge and data related to the algae’s capabilities to form toxins increases. In Delaware, as elsewhere, dense blue-green algae blooms also contribute to lowered levels of dissolved oxygen, which can lead to fish kills.

 Toxins from blue-green algae have been documented in waters in other parts of the country where the algae is not visible or in full bloom. The problem is global as well as local and is being addressed in many other countries as scientific knowledge and data related to the algae’s capabilities to form toxins increases. In Delaware, as elsewhere, dense blue-green algae blooms also contribute to lowered levels of dissolved oxygen, which can lead to fish kills.  

 

 

 




 

 

 

 

 

 

 

 

 

 

 

 Paint-like scum formed by a blue-green algal bloom floating on top of murky, pea-soup green water.  Photo: Edythe Humphries

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Paint-like blue-green algal scum floating amidst fallen tree leaves on top of relatively clear water.  Photo: Robin Tyler

Above: Paint-like blue-green algal scum floating amidst fallen tree leaves on top of relatively clear water. 

Degraded paint-like blue-green algal scum associated with a very heavy bloom near a shoreline. Photo: M. Higgins

Degraded paint-like blue-green algal scum associated with a very heavy bloom near a shoreline. Note the “clumpy” appearance of the scum and whitish and blue-green colors. This appearance is typical of early-fall conditions when blooms are beginning their seasonal die-off.

Additional examples of a degrading blue-green algal bloom during early fall.  Photo: Robin TylerAdditional examples, above and below, of a degrading blue-green algae bloom during early fall. 
Another example of a degrading blue-green algae bloom during early fall. Photo by Robin Tyler

 

 

 
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