History from the Philly Watersheds Page:
Most of the watershed of the Wissahickon, a tributary of the Schuylkill River, is located in suburban Montgomery County. Within the city limits the creek has two major tributaries. Cresheim Creek still flows on the surface, while all but the lower reach of Monoshone Creek was encapsulated in a separate sewer in the early 20th century, with Lincoln Drive winding over part of this stream’s former course.
In order to protect the city’s water supply, which was then mostly drawn from the Schuylkill at the Fairmount Water Works, the Wissahickon Valley within Philadelphia was made part of Fairmount Park in the late 1860s. With this purchase, not only was this beautiful 1,800 acre gorge protected from development, but dozens of mills that had used the creek for water-power were one by one condemned and torn down. Today, occasional picturesque ruins provide the only reminders of the valley’s former industrial history.
Co-existing with the mills in the 1800s were numerous taverns and roadhouses, one of which, the Valley Green Inn, remains open today. Celebrated in the 19th century in poetry and prose for its wild beauty, the Wissahickon is still one of the most scenic areas of the city, and is heavily used for recreation.
Interceptor sewers were built through the Wissahickon Valley in Philadelphia beginning in the 1880s and continuing into the first decades of the 20th century. These sewers captured the sewage flowing from neighborhoods at the top of the valley and were designed to intercept it before it entered the creek. A major interceptor pipe parallels the hiking trail on the east side of the creek, most of this pipe runs underground, but a concrete arch bridge near the mouth of Cresheim Creek—the Cresheim Aqueduct—carries this interceptor across the Cresheim valley.
Since the bulk of the Wissahickon Creek watershed lies beyond the city limits, the quality of the water in the stream depends mainly on the actions (or inaction) of suburban municipalities. Even within the city, the Fairmount Park purchase did not encompass the entire watershed from ridge to ridge, and development in the higher parts of the watershed has led to problems in the valley below. Many tributary streams have been badly eroded by stormwater drainage from streets and private property outside the park. While development within the city is mostly complete, in the suburban reaches of the watershed open land continues to be developed, exacerbating storm flooding. Several upstream municipalities also discharge treated sewage effluent into the creek, and in dry weather much of the stream flow is made up of this effluent.