6 July 2025
Should you’ve been to Schenley Park’s Panther Hole Lake on any sizzling summer time day prior to now decade you’ve seen its floor lined in vivid inexperienced soup and lumpy, slimy pond scum.
Look intently on the inexperienced soup and also you’ll see that it’s duckweed (Lemnoideae), a floating plant made up of tiny leaf-like buildings, every dangling a tiny root.
The lumpy scum is filamentous algae made up of single cells in lengthy threads. It grows on the underside of the pond, ultimately clumps collectively and floats to the floor. It smells dangerous within the warmth. Sure, it’s nickname is “pond scum.”
In small quantities native duckweed and algae are helpful. Duckweed is meals for geese and wildlife. Algae, when it decomposes, is meals for invertebrates. Each present hiding habitat for underwater wildlife.
However in sunny warmth these two organisms develop enormously, cowl the floor after which …
Algae and duckweed produce oxygen as a by-product of photosynthesis. That is important for aquatic creatures. At evening or when daylight shouldn’t be out there, nonetheless, the vegetation eat oxygen. In sure circumstances, the quantity of oxygen getting used can exceed the quantity being produced, and thus ends in oxygen depletion and fish kills. This usually occurs throughout sizzling summer time months, when the water is hotter and unable to carry larger quantities of oxygen, or on cloudy days, when there may be minimal solar.
— Brandywine Conservancy: Algae & Duckweed: The Prices and Advantages
In late June’s extreme warmth Panther Hole Lake suffered the associated fee. I used to be out of city when Andy Georgeson despatched me this message and two pictures of a fish kill in progress.
[At Panther Hollow Lake on 25 June 2025] I seen a distinction, even from Monday, once I was final there to right now. The fish appear like they’re actually struggling and near dying. They have been all crowded close to the shore that was nearer to the practice tracks and appeared to be gasping for air with little or no motion.
— electronic mail from Dr. Andy Georgeson, 25 June 2025
Fish look like bluegill, pumpkinseed and 1 catfish (black)
By the point I visited on Wednesday 2 July, the Division of Public Works had eliminated the lifeless fish. I discovered many dwell fish — greater than traditional — within the influx close to the cattails.
As well as, on this picture I counted 9 circles on the underside of the pond. Had been they made by fish for egg laying? Spawning?
Kids performed by Panther Hole Lake on Wednesday utilizing lengthy sticks to tug the filamentous algae out of the water and set it on the concrete edge.
The Underlying Trigger: Panther Hole Lake has summer time algae blooms as a result of it’s shallow and has an unnatural concrete edge that permits a number of runoff. Brandywine Conservancy’s #1 answer is to cease vitamins and sediment from operating into the lake by:
- Limiting fertilizer use. (Fertilizer shouldn’t be taking place close to Panther Hole Lake anyway.)
- Establishing wholesome vegetative buffers particularly, shrubs, native grasses and wildflowers, to catch and filter runoff. i.e. Take away the concrete edge.
In the meantime Panther Hole Lake is eutrophic as a result of it’s “outdated” within the regular life cycle of a lake. Learn extra at NHLakes: The Lifetime of a Lake.
p.s. A Tip of the Hat to Brandywine Conservancy’s nice article on Algae & Duckweed: The Prices and Advantages.
