Skip to Main Content

Harmful Algal Blooms

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:

Under the 'Change Dates' menu, type in desired date range (choose a range less than 31 days) and click the 'Go!' button, or by clicking the arrows your search will move forward or backward in time by 2 weeks. If no symbols appear in the map no data are available as yet.

For a full-screen map view click here

Eyes on the Bay - Interactive Mapping of Current Year Long-Term Station Data
Show Legend
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.

Filter/Find Species
Change Dates
Samples from

Please wait while the map loads...