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Little Falls Subwatershed


The Little Falls subwatershed is one of the County's most urban stream systems, with part of its drainage from the northwest portion of the District of Columbia. This subwatershed contains some of the oldest developed areas of the County. There are several historic elements in the subwatershed, such as Battery Bailey (a landmark fortification from the Civil War), the route of the old trolley line, the Washington Aqueduct, and the C&O Canal, all of which have played a role in shaping the subwatershed's landscape.

Image of Little Falls Watershed

A Journey Through the Little Falls Watershed

Most of the development in this subwatershed occurred before today's requirements for natural stream buffer, wetland, and floodplain protection and for stormwater runoff controls. The original drainage pattern of Little Falls has been extensively altered, with much of the original headwaters and tributaries enclosed in storm drain pipes or channelized. What remains of the headwaters now receives drainage from highly impervious areas in the Bethesda Central Business District and Friendship Heights.

Channelized and piped areas throughout the subwatershed deliver flows into downstream channels at accelerated velocities and often with very high temperatures after flowing through open concrete channels or across paved surfaces warmed by the summer sun. These stormflows seriously impact the remaining natural channels downstream.


Image of the C & O canalHealth of the Subwatershed

Several catastrophic pollution events have also influenced subwatershed conditions, including:

  • a large oil spill that ignited and burned for two days in 1959 (melting the Massachusetts Ave. Bridge)

  • chlorine discharges associated with treatment of drinking water supplies

  • chronic sewer line problems, and

  • an underground oil leak that has been repaired.

As a consequence of inadequately controlled runoff and periodic pollution events, stream resource conditions are poor, with the exception of the lower reach of Little Falls below MacArthur Blvd.

A study conducted in 1976 found no life in Little Falls (Dietermann 1976). In 1994, the Maryland Biological Stream Survey found 4 species of fish in the lower mainstem below MacArthur Blvd. Above Massachusetts Ave., only three individuals of the very pollution-tolerant blacknose dace were found. Since then, stream bug (macroinvertebrates) species found above MacArthur Blvd. are all pollution-tolerant. Below MacArthur Blvd., the macroinvertebrate population is somewhat more diverse, but the number of individuals, or abundance, remains low.

Because of the highly developed nature of the subwatershed, few site opportunities exist to add remedial stormwater controls. Possible incremental restorations that could improve conditions, particularly water quality, could occur. Now that water pollution impacts are being better managed, biological resources in this subwatershed may very well be on the verge of a turnaround, particularly in the lower mainstem where habitat conditions can still support an aquatic community.

The best opportunities for restoring a more balanced aquatic community are in the reaches from Massachusetts Ave. downstream to the Potomac River. This area still contains stream habitat capable of supporting fish, aquatic insects, and other aquatic organisms. The high population density and many recreational opportunities, including the extensive trail system and linkage to the National C&O Canal Park, make this area a potential showcase of our ability to blend urban life with the natural environment.


How Can I Help Protect the Little Falls Subwatershed?

Individuals interested in helping to protect the health of the Little Falls subwatershed can contact the Little Falls Alliance. This organization of local citizens prides itself in protecting and improving the streams within the Little Falls subwatershed.

         Flow of the C & O canal           History at the C & O canal