Baltimore Harbor bacteria map

  • 2009 only Includes partial measurements, shown as white rows
  • 2009-2011Omits partial measurements

Which parts of Baltimore's harbor are the most polluted? A 2009 survey by the city and the Baltimore Harbor Waterkeeper, part of a non-profit watchdog group, helps to provide the answer. For days when a bacteria count was taken, the charts below show the percentage of days the count was below the state's threshold for regular swimming (green), above the threshold for regular swimming (yellow) and above the threshold for even infrequent immersion (red).

To see a complete list of readings for a site, click on a pie chart. A list will appear to the right showing the location and dates of sampling, plus enterococci bacteria counts for days a reading was taken. The table also lists the amount of rain and period of time it fell before the sample was taken. That's important because heavy rains tend to flush more pollution into the water.

Note that because of the pie charts' size, represented locations are approximate. Click one of the two tabs above to choose the version of the map that you wish to see.

Bacteria levels are low enough to meet the state's limit for regular swimming — a "most probable number" of 104 colonies of enteroccocci per 100 millileters of water.
Bacteria levels are above the threshold for regular swimming, 104 colonies per 100 millileters.
Bacteria levels exceed the threshold for even infrequent immersion, at 500 colonies per 100 millileters.

The state Department of the Environment and some local health departments regularly monitor the bacteria levels at bathing beaches around Maryland, but don't do so in Baltimore because there are no officially recognized swim spots in the harbor or its tributaries. Nevertheless, on its website, the city health department carries a recommendation against swimming anywhere in the harbor and urges boaters to wash their hands before eating or after leaving the boat.

Data Credits: Baltimore City Department of Public Works and the Baltimore Harbor Waterkeeper.
Programming: Edin "Dino" Beslagic with minor additions by Patrick Maynard. Reporter: Timothy B. Wheeler