The Questions:
bryozoanRhonda, East Tennessee, USA – I found this in an East TN lake, between 1-3 feet down, attached to underwater pine branches, gelatinous and slimy to touch. Frog’s eggs or bryozoans? (see photo at left)George, Ontario, Canada – I was cleaning the weeds from around our boat and saw two opaque jelly-like substances just below the surface of the water (looked like jelly fish) among the weeds. I caught one on the fork and removed it with the weeds, the other one quite large in size like a small football slipped of the fork and escaped. This was in the Trent canal system in the Bobcaygeon area. Has anyone else seen anything like this?

Marcus, USA – We recently found one of these blobs, too, around our beach as we were cleaning the weeds. I was interested in finding out what it is.

(click on photos and graphics to expand)

"Pectinatella magnifica 8568" by Jomegat

Freshwater bryozoan (photo by Jomegat)

The Short Answer: I thought I’d respond to these all together since these have all come in the last few days. In all three cases, it’s almost certainly the bryozoan Pectinatella magnifica. I wrote an article on these a while back:

What is this jelly-like blob under my dock

The photograph Rhoda sent is definitely a bryozoan colony and I feel pretty confident in saying that the others are as well because the only other large blob-like things commonly found in fresh water in North America are amphibian egg masses. But as these three reports came in mid-late August, that’s very unlikely. Most amphibians lay eggs in the spring. And the descriptions are pretty classic bryozoan, with softball to football-sized jelly-like blobs found around docks and swimming areas.

Here’s another site with good info:


Pectinatella magnifica (photo by Triclops200)

Pectinatella magnifica (photo by Triclops200)

More Information: I’m wondering why I received all three of these reports within a week of each other.  It could be simply chance, of course.  Or maybe it’s just that after a summer of growing, the bryozoan colonies are larger and more visible now.  Another possibility is that I have noticed in the lake I live on the water begins to clear at this time of year (mid-August).  I assume this happens because the algae, diatoms and other plankton populations start to die back as nights get colder and the day length is growing shorter.  It’s still hot, so we think of this as being still summer, but the longest day of the year was two months ago, so for the microscopic plants and animals at the bottom of the aquatic food chain, the peak growing season is past.  With less life going on in it, the water is less cloudy and people can see things underwater more clearly.

Maybe that’s the simple explanation.  As the water clears, people suddenly say, “What’s that jelly-like blob under my dock?”

Ask a Naturalist® (November 30, 2023) Jelly-like blob under the dock – part two. Retrieved from
"Jelly-like blob under the dock – part two." Ask a Naturalist® - November 30, 2023,
Ask a Naturalist® August 22, 2011 Jelly-like blob under the dock – part two., viewed November 30, 2023,<>
Ask a Naturalist® - Jelly-like blob under the dock – part two. [Internet]. [Accessed November 30, 2023]. Available from:
"Jelly-like blob under the dock – part two." Ask a Naturalist® - Accessed November 30, 2023.
"Jelly-like blob under the dock – part two." Ask a Naturalist® [Online]. Available: [Accessed: November 30, 2023]