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Blue-Green Algae in Delaware
Blue-green algae – also known as cyanobacteria – are naturally occurring microscopic 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. Although there have been no reported cases of human or animal illness in Delaware associated with exposure to blue-green algae, a team – comprising scientists, biologists and other subject matter experts from DNREC, the Division of Public Health and the Department of Agriculture – was formed to review scientific knowledge of the state’s recreational lakes and ponds and develop water advisories as a common-sense, precautionary measure for the public.
The team also developed a water advisory sign that will be placed at select lakes and ponds throughout Delaware alerting the public to the presence of blue-green algae and its possible harmful effects on people and animals.
In 2006, DNREC issued a news release during a blue-green algae bloom on Silver Lake in Dover, which lingered for weeks and gave the water the characteristic "pea green" color after forming a scum on portions of the lake’s surface. The high coloration caused some residents to report a suspected paint spill.
Since then, laboratory results from a single-day sampling during a bloom indicated elevated levels of the blue-green algal toxin in laboratory results. Although a sample taken the following day showed no elevated levels of the toxin and, as noted above, no human or pet illnesses associated with the blue-green algae have been reported in Delaware, the committee was constituted to address potential health effects.
The best precaution is to avoid contact or exposure to water with blue-green algae blooms or scum and if contact s 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.
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 or swallowed water containing high concentrations of blue-green algae include, from inhalation: 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.
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.
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