23 August 2026
On Thursday 20 August, in 45 minutes from 8:10 and 8:55am, it rained 1.55″ at the Allegheny County Airport. For almost 15 minutes it came down at the rate of 3.4″ per hour. Schenley Park’s Panther Hollow Lake was one of many waterways that overflowed. By Friday morning the flood waters had receded, leaving behind a coating of duckweed right up to the high water mark. This was the first time I’ve ever seen a duckweed flood.
Ideally the flood would have been handled by the old concrete overflow channel but it’s blocked by a landslide so the flood ran over the channel edge and down the path to the lake.
Water scoured new ditches and carried an old orange cone into the lake. It also beat down the cattails on its way to the duckweed zone.
Because Panther Hollow Lake is pond-sized and very shallow it is eutrophic in the summer, covered in duckweed and filamentous algae. On the lake, everything was a sea of green.
Duckweed heavily coated the concrete edge, …
… and a lumpy log right next to the edge …
… and the grass.
Usually duckweed (Lemnoideae) is a floating plant with each tiny leaf-like structure dangling a tiny root. But the water is gone. The leaflets are stuck to everything.
Will it take another rain storm to wash away the duckweed? Or will the sun desiccate it and make it brown? I’ll have to go back and see.
The condition of the Schenley trails appears to be deteriorating this year.
Heavy rain has certainly caused trouble on the trails. I’ve also noticed more large trees just falling over at the root ball this year. Not caused by wind it’s that the soil is so wet that and any leaning tree with poor root-hold just collapses.
If you look closely at the photo of duckweed on grass, you will see tiny green “dots”. I believe they are Watermeal, or Wolffia, the world’s smallest plant.
Wow!