A watershed is “the land area through which water flows and drains to the lowest point, into a stream, river, lake, or estuary. A watershed may be large or small, may occupy sloping, mountainous or nearly flat terrain, and may cover many landscapes, including forests, farmland, small towns, and cities. Human activities in a watershed eventually affect the water quality downstream.”
-The State of the Chesapeake Bay and Its Watershed, The Chesapeake Bay Program

From the time of settlement, the Jones Falls river served Baltimore City as a transportation corridor, a power source for early industry, and a source of drinking water (learn more about Jones Falls history). Though history tells of a wealth of wildlife that once lived in the river valley, the stream is more often thought of for its role in the development of the area. In particular, the river lends its name to the I-83 expressway, one of the primary transportation routes into Baltimore City. The highway parallels the Jones Falls before the river flows into a tunnel near Penn Station. The Jones Falls emerges at Fayette Street and, within a few blocks, joins the Baltimore Inner Harbor. Today, the lands that comprise the 58-square-mile Jones Falls watershed mirror the larger Chesapeake Bay watershed in many ways. The upper portion of the watershed is primarily rural. Development is limited by zoning and by the Urban Rural Demarcation Line (URDL), the boundary that establishes the extent of city water and sewer lines. Property outside the URDL must rely on septic systems for the disposal of waste and on wells for water. Areas serviced by sewer and water are more heavily developed. In the city portion of the watershed, most of the streams have been buried, piped, and converted to storm water drains. Stream health in the Jones Falls declines with the increase in development. The watershed contains more than 267 miles of streams and 330,000 linear feet (63 miles) of gravity sewers. It is home to more than 230,000 residents. The 2000 Chesapeake Bay Agreement lists the Jones Falls as impaired waters and, with the Inner Harbor, as a priority urban waterway. Despite the impacts and pressures of development, the stream valleys and even sections of the river that parallel the Jones Falls Expressway provide important habitat for area wildlife and a scenic respite for area residents.

The upper reaches of the Jones Falls watershed, which are more rural, support reproducing trout populations. Trout are a cold water fishery and are sensitive to changes in stream temperature and sedimentation. These Baltimore County subwatersheds are on the threshold at 8-10% impervious cover. Models predict that watersheds with greater than 10% impervious cover are unable to sustain the water quality required by such sensitive species as trout. For now, these properties lie outside the Urban Rural Demarcation Line and have been protected from much development by zoning restrictions. Additionally, 2,363 acres have been protected through environmental easements that land owners have placed on their properties to retain the rural landscape. However, as the land around these areas is developed, pressure increases to develop the remaining parcels. In urban portions of the watershed, only the most tolerant macroinvertebrate insect species survive.