Mass. Gen. Laws ch. 58 § 17B
The state treasurer shall annually, not later than November twentieth, upon certification by the commissioner as hereinafter provided, pay to each town in which property has been taken for flood control reservoirs by the commonwealth under any act, or the United States pursuant to consent granted by the commonwealth under chapter two hundred and eighty-four of the acts of nineteen hundred and thirty-nine, chapter five hundred and ninety-four of the acts of nineteen hundred and forty-eight and chapter six hundred and thirteen of the acts of nineteen hundred and fifty-six, an amount determined by the commissioner as tax losses resulting from the takings. Such losses of taxes as determined by the commissioner shall be based on the then current tax rate in each town in which property has been taken for flood control reservoirs and on the average assessed valuation for a period of five years prior to the acquisition of said land; provided, however, that whenever a town wherein a flood control reservoir or portion thereof is located shall have made a general revaluation of property subject to the annual municipal taxes for such town, the commissioner may use such revaluation for determining the taxes for which payment shall be made. Said commissioner shall annually ascertain said valuation and the amount to be paid to each town, and shall certify the same to the state treasurer not later than November first.
Mass. Gen. Laws ch. 58, § 17B