Section 2.
The City of Boston shall cause said pond to be cleaned of such impurities prejudicial to the public health, as in the judgment of the State Board of Health Lunacy and Charity, it shall have caused . . . and should the said Board deem the same to be necessary and so decide, the City of Boston may erect a dam at the outlet of the Mystic Lower Pond, and exclude the tide water from said pond, and may raise the height of the water in said pond and may take land therefor.
