"Sometimes you see little bits of oil on the water, but this is more than I've ever seen," he said. "It's like rowing through a gas station."
He said that he noticed it Monday at the twin stone bridges in East Falls and that it had moved to the Columbia Avenue Bridge by yesterday.
John Hogan, 57, the commodore of the Schuylkill Navy, which is the governing body of the boathouses on Boathouse Row, said dozens of people have come to him with concerns.
"It's disgusting and it smells like diesel fuel," he said. "There was heavy, dark, icky stuff on the boats that had to be scrubbed off once you got them out of the water."
Laura Copeland, spokeswoman for the Water Department, said that the agency believes the substance could be hydraulic oil.
She said that there was more than 10 gallons of it spread along the river and that most appeared to be hugging the east side. The substance has not been detected near the department's intakes for drinking water, which are on the west side of the river, she said.
However, Urevick-Ackelsberg said he saw the substance "coating the river from the west side to the east side."
Copeland said the department's treatment plants would clean the water before it gets distributed.
She said that the department hasn't found the source of the spill and that it appears to have stopped, which will make locating it even more difficult.
But Deborah Fries, spokeswoman for the DEP's regional office, said their preliminary investigations found that the entry point was the Water Department's Dobson's Run storm-relief sewer, a $36.4 million project completed in June that rerouted the small stream of Dobson's Run into the Schuylkill. The project, initiated to prevent flooding, kept two lanes of Kelly Drive closed for three years.
Copeland said the Water Department is testing samples of the tainted water. In the meantime, she urged anyone with information on this or other situations to contact the department's hot line at 215-685-6300.