Merrymeeting River & Lake
MERRYMEETING RIVER & LAKE WATERSHED MANAGEMENT PLAN FOR THE CYANOBACTERIA MITIGATION STEERING COMMITTEE OF NEW DURHAM/ALTON [FINAL September 2019] FB ENVIRONMENTAL ASSOCIATES 170 West Road, Suite 6 Portsmouth, NH 03801 www.fbenvironmental.com © John Gisis MERRYMEETING RIVER & LAKE WATERSHED MANAGEMENT PLAN FB Environmental Associates ii MERRYMEETING RIVER & LAKE WATERSHED MANAGEMENT PLAN MERRYMEETING RIVER & LAKE WATERSHED MANAGEMENT PLAN Prepared by FB ENVIRONMENTAL ASSOCIATES in cooperation with the Cyanobacteria Mitigation Steering Committee of New Durham/Alton, DK Water Resource Consulting, and Horsley Witten Group FINAL | September 2019 CONTACT Cyanobacteria Mitigation Steering Committee of New Durham/Alton P.O. Box 243 New Durham, NH 03855 Funding for this project was provided by the towns of New Durham and Alton, New Hampshire. FB Environmental Associates iii MERRYMEETING RIVER & LAKE WATERSHED MANAGEMENT PLAN EXECUTIVE SUMMARY According to the 303(d) New Hampshire List of Impaired Waters, Marsh, Jones, and Downing Ponds are impaired for primary contact recreation due to elevated levels of cyanobacteria hepatotoxic microcystins. Toxic cyanobacteria blooms are often indicative of enhanced nutrient loading, particularly phosphorus, from point source (PS) and nonpoint source (NPS) pollution such as stormwater runoff from developed and agricultural land uses. In this case, point source discharges from the Powder Mill State Fish Hatchery are estimated to contribute 342 kg P/yr (67% of the total load) to the river as it flows into Marsh Pond. Local groups and town officials are working with state and federal agencies to set an appropriate phosphorus load discharge limit for the Powder Mill State Fish Hatchery; this permitted limit will dictate the achievable in-pond concentrations for Marsh, Jones, and Downing Ponds, and thus, the water quality goals described herein should be considered preliminary.
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