by Sally Soule, former NRWA Environmental Education
Citizens in the Nashua River watershed depend
on its waterways for drinking water, recreation, waste removal,
and aesthetics. Plants and animals also depend on the waterways.
In order to protect aquatic habitats and waterways from degradation,
it is essential that watershed residents understand the connection
between land use, water quality, water quantity and aquatic habitat.
A waterways physical, chemical and biological features determine
aquatic habitat. Biologically diverse waterways are considered to
be an indicator of healthy aquatic ecosystems.
Human actions on the land and in the river directly
affect aquatic habitats. Sedimentation caused by stream bank erosion
and runoff can smother substrates necessary for aquatic life. Sedimentation
can also lower water clarity, which eliminates sunlight needed by
aquatic plants for photosynthesis. Polluted runoff can contribute
nutrients that accelerate plant growth and lower dissolved oxygen
levels. The removal of vegetation along riverbanks can lead to erosion
and increased temperatures due exposure of the waterway to sunlight.
Bacteria from failing septic systems and agriculture can introduce
pathogens that can threaten human health and recreational uses of
the river.Alterations of natural flow regimes in river and streams
and water levels in other non-flowing hydric habitats can degrade
their value for aquatic and other water-dependent organisms.
The Nashua River watershed drains 538 square miles in the central
highlands of southern New England. The river has two main branches:
the North Nashua River, which is formed by the junction of the Whitman
River and Flag Brook in West Fitchburg, MA, and the South Nashua
River, which flows from Wachusett Reservoir. The North and South
Nashua Rivers meet in Lancaster, MA and form the Nashua Rivers
Main Stem. Two major tributaries, the Squannacook and Nissitissit
Rivers, join the Main Stem and contribute a significant amount of
flow. These tributaries are fed by a series of smaller streams that
originate in the watersheds upper reaches. Smaller waterways
such as Catecunamaug, Unkety and Mulpus Brook also flow into the
Main Stem. The Main Stem flows north to join the Merrimack River
in Nashua, NH.
The rivers headwaters and tributaries begin
in terrain that is formed by rolling hills, which are more rugged
to the north and west. The Main Stem flows through the Nashua River
valley, which follows a broad flood plain, bordered by hills. The
landscape shows the effects of the movement and melting of glaciers.
During the last ice age, rocky soil was deposited in the uplands,
while the lowlands were buried in sand and gravel carried by glacial
melt water. The watershed has a broad range of soil types, which
support a diversity of plant communities. This topography helps
shape the aquatic habitat of the watersheds tributaries and
The climate of the watershed is typical for central
New England. Temperatures range from ninety-five degrees Fahrenheit
to minus twenty degrees Fahrenheit. Precipitation averages about
forty-four inches per year, although slightly less falls in the
summer. Approximately forty-four percent of the precipitation is
lost as evapotranspiration and the remainder is divided between
surface runoff and ground water discharge.
Nashua River Main Stem
The Main Stem flows slowly at a low gradient over flood plains,
which contain glacial deposits of sand and gravel. River depths
range from less than two meters to over ten meters. The substrate
of the Main Stem is generally silty with layers of fine organic
material. Some sand deposits are present. Riffles in fast flowing,
shallow areas exist at several locations including the Rt. 111 bridge
in Hollis, New Hampshire and downstream from the Ice House Dam in
The aquatic habitat and hydrology of the Main Stem
are influenced by several impoundments created by dams. The impoundments
slow the rivers flow even further and create lake or pond-like
areas prone to warm water, low levels of dissolved oxygen, algal
blooms, and dense aquatic plant growth. Several impoundments are
known to contain infestations of nuisance aquatic plants. The impounded
areas also serve as a sink for sediments; some of which may be leftover
from point source discharges in the 1960s and earlier.
The Main Stem supports an abundance of fish species associated
with warm water fisheries such as largemouth bass, bullhead, and
perch. Large woody debris are common in the river and are important
habitat features that provide shade for fish, perching places for
birds, and resting areas for turtles. Several oxbows on the Main
Stem offer habitat for waterfowl and mammals. Kingfishers, herons,
beavers, and muskrat are common along the waterway; mink and river
otter have also been seen.
Riparian Corridor and Land Use
The riparian corridor is dominated by wooded or open land interspersed
with areas of residential and industrial development. Significant
portions of land along the Main Stem are protected by state, federal,
or local agencies. Some areas of the river are densely forested
with oaks, pines, and maples. In these reaches, the overstory provides
a canopy that shades the river and keeps water temperatures relatively
low. These are important areas for fish. In places where the river
is wide, the riverbanks support herbaceous vegetation such as cattail,
woolgrass, and purple loosestrife (invasive).
Aquatic Habitat Concerns
- Recreational fishing is a common activity on the
lower Main Stem. However, large boats and motors can churn up
bottom sediments, which affect water clarity, and accelerate streambank
erosion. Large motor boat noise and/or wakes can also intimidate
wildlife from using or remaining in what is otherwise suitable
- At this time there are no fish ladders to ensure
passage for fish at any of the dams on the Nashua River Main Stem.
Anecdotal evidence suggests that fish attempt to move from one
impoundment to the next, but are thwarted by several dams.
- Nonpoint source pollution continues to threaten
the rivers chemistry and habitat; sedimentation and nutrients
are key concerns.
- Invasive species such as purple loosestife and
water chestnut pose a threat to the rivers riparian corridor
and aquatic habitat.
Nashua River Tributaries
General Physical Description
Many of the rivers main tributaries begin in the moderate
to steep topography of the north and west regions of the watershed.
Bedrock outcrops and predominantly till or hardpan soils dominate
the watersheds upper reaches. These characteristics generally
create impervious areas, which prevent infiltration, and lead to
heavy run off, flashy peak flows, and dry weather flows
that are substantially below average. Flooding, erosion, and sediment
transport are also evident and indicative of the topography and
geology. Many tributaries possess desirable riffle/run/pool habitat
ratios, which are critical for aquatic life. Riffles are mixing
areas that provide food and oxygen to the stream life; runs consist
of deeper, swifter stretches of the stream where fish can travel;
and pools offer important resting places for fish and wildlife.
Most tributaries flow into the rivers Main Stem
from the north, south, and west. Very few flow to the river from
the east and those that do such as Unkety, James and Nonacoicus
Brooks originate in more level terrain, have slower flow regimes,
and are associated with wetlands.
Tributaries to Wachusett Reservoir such as the Stillwater
and Quinapoxet Rivers generally possess exemplary aquatic habitat:
riffle/run flow regimes, cobble substrates minimally affected by
sedimentation, high percentage of canopy cover, and sustained flow.
Fortunately, the Metropolitan District Commission's protection of
the tributaries has a side benefit of protecting aquatic and riparian
habit as well.
Many of the watersheds tributaries are biologically diverse.
The Squannacook and Nissitissit Rivers are both considered by the
state to be Outstanding Resource Waters. This designation affords
protection for the high level of aquatic habitat found in both waterways.
Cold water fish species such as brook trout can be found in many
tributaries, and cool temperatures afforded by forest canopy and
low levels of dissolved oxygen also support many species of aquatic
insects and invertebrates. Several species of freshwater mussels
can be found in the basins tributaries. Mussels are generally
considered by to be biological indicators of water quality and aquatic
habitat. Many freshwater mussels species are thought to be in decline
due to habitat loss and alteration. Mammals such as otters, moose,
and beaver are also present in and near many tributaries.
Biological diversity is compromised by polluted runoff, point source
pollution (combined sewage overflows), sedimentation, loss of vegetated
buffers, and channelization and alteration of natural flow regimes
in several tributaries that flow through highly urbanized areas
such as the North Nashua River, and some portions of Monoosnoc,
Falulah, and Phillips Brooks.
Riparian Corridor and Land Use
Many tributaries such as the Whitman, Squannacook and Nissitissit
Rivers flow through forested lands with little residential or commercial
development. For these waterways the diversity of vegetation types
provides ample cover and food for invertebrates, which provide food
for fish and other wildlife. Riparian areas adjacent to tributaries
serve as natural buffer zones, which protect water quality and provide
A few streams, including the North Nashua River, flow
through highly developed areas where streamside vegetation is sparse
and the waterway is exposed to direct sunlight and urban impacts.
Aquatic Habitat Concerns
- Water withdrawals may adversely affect many of
the basins smaller tributaries such Mulpus, Catecunemaug,
and James Brooks.
- Sedimentation from road runoff and development
may be present in smaller tributaries.
- Alteration of streamside vegetation adversely affects
urban tributaries in certain reaches.
Aquatic life in rivers and streams depends on the quality and quantity
of available habitat. The Nashua River watersheds rivers and
streams contain a range of aquatic habitats that support a diversity
of plant and animal life. For example, the Squannacook and Nissitissit
Rivers are renowned for their recreational cold water fisheries
and pristine beauty. During the past one hundred years as land use
in the basin has shifted from agriculturally based activities to
residential and industrial uses the landscape and ecology of the
Nashua River watershed has changed dramatically. Presently, habitat
loss, polluted runoff, and increased water withdrawals threaten
aquatic species in the Nashua River and its tributaries. Protection
of the Nashua River watersheds riparian corridors and the
adjacent upland from unplanned development is essential for maintaining
high levels of aquatic habitat.