Where the Delaware River flows past South Philadelphia, an unnamed island offers an expansive view of oil storage tanks and a commercial shipyard on the Pennsylvania side, while a procession of jets land at Philadelphia International Airport about two miles away.

But on a warm and sunny summer afternoon, the industrial landscape was of no concern to several families of boaters who had pulled up to the island to laze in the sunshine, wade on a small beach, and swim in a river that was once badly polluted and is still thought of that way by many in the region.

As Jet Skis sped past and other pleasure craft bobbed in the water, the boaters acknowledged the river’s history as an “open sewer” for industrial effluent and human waste, but said they are now sufficiently comfortable with the water’s improved condition to allow their families to swim and play in it.

“We come down on the weekends, anchor up, take a swim,” said John Szumowski, 41, a contractor from Philadelphia, as his daughter floated in a tube a few feet away from his boat. “I have my family out here all the time, and we never have any problems.”