Algae Bloom Health Advisory Lifted for the Charles River

BOSTON - October 9, 2024 – The Boston Public Health Commission (BPHC) is alerting residents that the Massachusetts Department of Public Health (DPH) has lifted the public health advisory issued for the Charles River, downstream of the Longfellow Bridge. This advisory was put into place on September 24. Analysis of testing samples taken in the area on September 30 and October 7 demonstrated cyanobacteria levels below the state’s safe limit of 70,000 cells/milliliters (mL) of water.  

DPH issued the public health advisory for impacted areas including the Broad Canal, Lechmere Canal, and Lederman Park areas, due to a bloom of blue-green algae also knows as cyanobacteria. On September 20 a visual assessment of the river, conducted by DPH staff, identified the presence of cyanobacteria cells at levels exceeding DPH guidelines for recreational waterbodies in Massachusetts.  

DPH generally recommends lifting recreational water advisories when two consecutive weekly samples show cyanobacteria counts below the safe limit of 70,000 cells/milliliters of water.  

On October 7 levels showed 35,000, 37,000, and 60,000 cells/mL for Broad Canal, Lechmere Canal, and Lederman Park, respectively. As this is the second consecutive result below the state’s threshold for unsafe conditions, the advisory is now lifted. The toxin microcystin was not detected in any of the three samples. 

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