If you’ve passed the Schuylkill River recently, you’ve probably noticed the unusual lime-green splotches covering the water along the banks.
“I didn’t know what it was, I really didn’t,” said 85-year-old Edward Carroll, who takes regular walks along the river. “It’s like, mushy. You know?”
“It looks like grass,” said Kim Adu, another seasoned walker. “Like, you could probably go golfing on it, but clearly that’s not what it is.”
And it’s not slime.
The carpet of green is actually a web of teeny-tiny aquatic plants called duckweed (lemna minor). Such a sight might seem alarming at first glance, but environmental scientists say it’s not harmful to humans or the river.
A frog makes its way through the thick duckweed on the Schuylkill River. (Emma Lee/WHYY)
“It’s actually an indicator of a healthy ecosystem along the river and inside the river,” said Kelly Anderson, an environmental scientist with Philadelphia’s water department. “You have many different species of animals that eat the duckweed. Not just ducks, but geese, snails, turtles, fish.”
Anderson said this level of growth hasn’t been seen here in over a decade. A lack of rainfall, low river flow, and warm air and water helped create a perfect environment for it to flourish. But, she added, it will likely dissipate with rainfall and cooler weather.