On August 29, 1820, a group of residents of Philadelphia and Northern Liberties wrote a letter to the Philadelphia County Board of Health about the polluted condition of Pegg's Run. Originally called Cohoquinoque Creek, this small but potent waterway was immediately north of Callowhill Street. It arose around current-day 15th Street and was fed by a spring near Ninth Street.
The stream was named after Daniel Pegg (ca. 1665-1702), a well-to-do Quaker brick-maker who once owned the ground in the area now know as the Callowhill East industrial district (the wasteland of parking lots between Vine and Spring Garden Street). The creek was said to have been navigable as far west as Ridge Road, about a mile in from the Delaware. Farmers would take their meats and produce on flatboats down this stream to deliver them to Philadelphia markets via the Delaware.
The pollution of Pegg's Run really was due to the fact that Philadelphia’s first manufacturing sector was located on the banks of the creek. Those early industries - breweries, slaughterhouses, soap makers, tanneries, and so on - discharged their wastes directly into the creek for outflow to the river.
Whatever the case, the letter that the neighbors of this area wrote was published in the Philadelphia Journal of the Medical and Physical Science:
Philadelphia August 29 
The present [letter] is to lodge information with you of the greatest nuisance in Philadelphia, we mean Pegg's Run, that putrid deposit of human excrements, corruptible matters of every kind, and every species of dead creatures. This, in time, will be the origin of serious consequences. Now we wish you to take into consideration that a bridge has been built in New Market Street over Pegg's Run. Whether it is owing to an error in leveling the bed of the creek, or to the non-removal of the dirt with which a bank was made to turn the waters, we cannot pretend to say; but what we can ascertain as fact is, that there is a pond of stagnated putrid water, a corruption to the air we breathe, a nursery for vermin, mosquitoes, gnats, &c. so as to make our houses nearly uninhabitable and unsafe for our health. We request you to take this, our complaint, into consideration, and exercise the power lodged with you to remove this nuisance. We remain with respect,
Heeding this public outcry, the Commissioners of Northern Liberties ordered that the creek should be turned into a sewer from Sixth Street to the Delaware. This work occurred in stages in the 1820s. But industries along the way simply obtained entrances into the culvert and continued releasing their refuse into the underground stream. Willow Street, a curvilinear street in a city not known for curvy streets, was laid on top of this sewer in the years before 1829.
The late 1960s Callowhill East Redevelopment Project eliminated most east-west streets and several north-south streets from the Philadelphia street grid in that locale. Out of necessity, however, the Willow Street Sewer had to remain, which is why Willow Street itself was not stricken from the grid. The sewer still flows to the Delaware at Pier 25 under Cavanaugh’s River Deck. The bridge that was "built in New Market Street" was once directly under modern-day I-95 in that vicinity.