The Gwynns Falls watershed (39.724847 N, -77.314183 W; 38.708367 N, -76.012008 W and approximately 17,150 hectares: site map) lies in Baltimore City and Baltimore County, Maryland and drains into the Chesapeake Bay. It contains 16 sub-watersheds, which range in size from 465 hectares to 1,855 hectares. The watershed’s resident population in 1990 was approximately 356,000 people. Total population and population density varied between sub-watersheds (from 18,360 to 109,187 people, and 2.5 persons / hectare to 19.8 persons / hectare in 1990) with the lower sub-watersheds of the Gwynns Falls being the most densely populated. During the last 40 years (1950 - 1990), total population and population density changed significantly in the Baltimore region because of movement of residents from the City and into the County (Baltimore City’s total population declined from a high of approximately 1.4 to 0.75 million). In the case of the Gwynns Falls watershed, total resident population declined in from 406,000 in 1970 to 356,000 in 1990; yet the percentage of urban areas increased from 66.3% in 1973 to 74.3% in 1990. Land use varies in the Gwynns Falls watershed: the lower sub-watersheds contained predominantly residential / commercial / industrial areas (90.4%) and the upper sub-watersheds contained primarily agricultural / forested / open space areas (90.8%) in 1990. The socioeconomic characteristics of residents in the watershed vary as well. For instance, the averaged median family income in 1990 was $18,598 in the lower sub-watersheds and $49,133 in the upper sub-watersheds.