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Archived Harmful Algal Blooms Map

Please note that cell counts from samples prior to 2015 should not be used for analytical purposes, as these were qualitative assessments based on live cell counts.
To view current HAB data please visit our HABs Map Page

To learn more about Harmful Algal Blooms (HABs) visit the Department of Natural Resources Phytoplankton Monitoring Program. To report algal blooms, please call (410) 260-8630, or report online using our Algae Bloom Sighting Report page.

Click on a station for more info and data:

Eyes on the Bay - Interactive Mapping of Current Year Long-Term Station Data
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Untitled Document
Algal Concentrations (cells/ml)
(small symbol) 0 - 3,000
(med. symbol) 3,000 -10,000
(large symbol) 10,000+


Bloom levels of concern

>3,000 cells/ml for Prorocentrum

>10,000 cells/ml for Microcystis, bluegreens, and Karlodinium


Algae are a natural part of our Bay ecosystems. Algae, like land plants, capture the sun's energy and support the food web that nourishes fish and shellfish. Algae may become harmful if they occur in an unnaturally high abundance or if they produce a toxin. Species of concern in MD include the the fish killing dinoflagellate, Karlodinium veneficum; the Mahogany Tide producing Prorocentrum minimum; the blue-green algae Microcystis aeruginosa (may produce liver toxins),as well as other potentially toxic bluegreen algae (may produce dermal, liver and/or neurotoxins).

Visit DNR's Harmful Algal Bloom page for more information.

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