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City Hall, 229 Main Street, PO Box 2019 Conservation Commission
Nashua, New Hampshire 03061-2019 Transportation
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589-3119
Date: April 4", 2018
To: John Griffin, CFO; Daniel Kooken, Purchasing Manager
From: Madeleine Mineau, Waterways Manager
Re: Contract for Aquatic Invasive Species Control and Management
Nuisance aquatic invasive plants are present in multiple Nashua water bodies, most notably the
Nashua River upstream of Mine Falls dam, the Mill Pond, and Nashua Canal. During summer
2017 the City also received several complaints regarding excessive plant growth in Sandy Pond
and the Waterways Manager documented that Curly Leaf Pondweed, an aquatic invasive species
was present in this pond. Aquatic invasive weeds, such as milfoil, fanwort, and water chestnut,
can make rivers and ponds unsightly, recreation unpleasant, and navigation by boat difficult.
Furthermore, excessive growth of vegetation can impair water quality due to reduced dissolved
oxygen which can cause fish kills.
The City’s Waterways Manager works closely with the State Invasive Species Coordinator at
NH DES to monitor the presence and extent of invasive species and update the Long-term Exotic
Aquatic Plant Management Plan for our waterways.
The City has been involved in controlling aquatic invasive species since 2011 when action was
taken to control Water Chestnut by mechanical harvest. This was very effective at removing
Water Chestnut and we now can continue to control Water Chestnut by hand pulling with
volunteers. Unfortunately, the decline in Water Chestnut created an opportunity for other
invasive species present in the River to take over. The vegetation is now dominated by milfoil
and fanwort which cannot be mechanically harvested or hand pulled, leaving herbicide treatment
as the only recommended effective management strategy. Herbicide treatments in rivers and
ponds are closely regulated and permitted which involves extensive public notice.
Herbicide treatments, which take place every other year, have been used in the Mill Pond and
Nashua Canal to control primarily milfoil and fanwort since 2012. Herbicide treatments cannot
eradicate these plants therefore, continued periodic herbicide treatments are necessary to knock
back the growth of these invasive species.
During summer 2017, herbicide treatments were used to control milfoil and fanwort on 84 acres
of the Nashua River upstream of the Mine Falls dam. This resulted in a very noticeable
improvement over 2016 conditions and we received multiple messages from constituents
reporting they were pleased with this outcome. Herbicide treatments are recommended again this
summer to continue reducing the coverage and extent of these invasive species in this section of
the Nashua River.
