Anyone using the boardwalk over the Schuylkill in South Philadelphia these days might be wondering what exactly the series of colored balls strung together and floating in the water are.

In fact, our former colleague Eric Ulken asked that question.

It is an installation called Tide Field by environmental artist Stacy Levy.

Part of the Mural Arts Philadelphia Art@Bartram's project, the current-driven buoys are meant to draw attention to the Schuylkill's tides.

Levy said she was still calibrating the buoys — recent flood waters have complicated things a bit —but when they are set,  multiple balls will be visible when the tide is low and only the yellow balls will show when it is high.

"They also move in the direction of the current," she said, noting the river rises and falls six feet twice a day.

"It's tricky working with a river," she said of the calibration efforts.

As Levy noted in her description of the installation: "The tidal fluctuation of the Schuylkill gives us a sense of the enduring quality of natural processes, occurring in the midst of our human world of concrete and steel. Having an understanding of the tidal timing and amplitude is a first step in creating a kinship with the river. Artwork can foster a deep engagement with the river…."