State health officials have confirmed a toxic algal bloom at Rosemary Lake in Needham, warning residents and pet owners to stay out of the water until further notice.
The Massachusetts Department of Public Health (MDPH) announced the confirmed cyanobacteria harmful algal bloom, or CyanoHAB, in a public health advisory Wednesday, Sept. 9. The bloom had been under investigation since late August, when the town posted warning signs after bright green algae appeared in the lake.
The advisory is blunt.
No swimming, no wading, no fishing. Keep dogs and other pets away from the water. Anyone who touches the water should rinse off immediately.
The Needham Health Department and the Park and Recreation Department first flagged the issue on Aug. 26, when MDPH began testing the lake for a possible bloom, according to an earlier town alert. At that point, the bloom had not been confirmed. The Sept. 9 advisory upgrades the status from possible to confirmed.
No timeline for lifting the Rosemary Lake advisory has been announced. The town said only that the warning remains in effect "until further notice."
Charles River advisory lifted
In a separate piece of good news for the area, MDPH has lifted the cyanobacteria advisory that covered a stretch of the Charles River running through Needham and Dedham since July 21.
That advisory covered the river between Kendrick Street and Nahanton Street in Needham and Newton to Bridge Street and Spring Street in Dedham and West Roxbury. It included Millennium Park and Cutler Park Reservation.
The advisory came down after two rounds of clean sampling met state requirements. MDPH tested the Charles River at the Millennium Park Kayak Launch on Aug. 17 and found cyanobacteria levels below the state guideline with no toxins detected, according to a Dedham public health update. A second round of sampling at multiple Millennium Park and Cutler Park locations on Aug. 24 also came back clean. Lab analysis detected no cyanobacteria, microcystin or cylindrospermopsin in any samples.
MDPH requires two consecutive rounds of results below its guidelines before lifting an advisory. The Charles River warning had been in place for roughly five weeks.
What residents should know
Rosemary Lake remains off-limits for all water contact. Residents with questions can reach the Needham Public Health Division at 781-455-7940 or [email protected]. Dedham residents with questions about the Charles River advisory can call the Dedham Health Department at 781-751-9220. More information about cyanobacteria is available from MDPH at mass.gov/dph/algae.
