What is this Jelly-like Blob Under My Dock?

The Question: I was swimming in the lake behind our house with a friend one day and we found a thing attached to our dock and it appeared to be brown fish egg sacks. But with closer observation it turns out to be a jelly like substance. What is it?

Submitted by: Kali, Tennessee
(click on photos and graphics to expand)
"Pectinatella magnifica 8568" by Jomegat

Freshwater bryozoan (photo by Jomegat)

The Short Answer: Without any other information or photos, it’s hard to be definitive about this, but usually, when people ask this question, what they have found is colony of the freshwater bryozoan Pectinatella magnifica. Freshwater bryozoans are tiny colonial animals that can form jelly-like masses, which are often found attached to sticks or docks.  Bryozoan colonies can be as much as a foot (30 cm) in diameter.

This Youtube video shows a couple of very nice bryozoans blobs:

Pectinatella magnifica (photo by Triclops200)

Pectinatella magnifica (photo by Triclops200)

Pectinatella magnifica

Pectinatella magnifica

More Information: Though they are not closely related to corals, bryozoans are superficially similar in that they are tiny colonial aquatic creatures that effectively filter particles from the water. The large gelatinous species is native to North America and often grows on docks and other submerged wood. During the summer it releases small larvae that swim away and establish new colonies nearby. In the fall each colony produces thousands of tiny, seed-like disks that remain dormant over winter and germinate the following spring. Most other freshwater bryozoan species form branching tubules that resemble brown moss in the water (Bryozoa = “moss animal”). While freshwater bryozoans improve water quality, some species become a serious nuisance when they clog intake and irrigation pipes.  For further information on freshwater bryozoans, the site of Dr. Timothy Wood at Wright State is very helpful: (My thanks to Dr. Wood for his help in preparing this answer.)

This Youtube video shows a very nice view of a bryozoan filtering food particles out of the water:

Cite this article as: Pelletier, TC. (September 16, 2010). What is this Jelly-like Blob Under My Dock? Retrieved from on May 27, 2016.

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25 Responses

  1. George Van Dyk Says:

    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 Bobcageon area. Has anyone else seen anything like this, does anyone know what I saw and has anyone else seen anything like this.

  2. Marcus Farrell Says:

    Yes we have recently found some too around our beach as we were cleaning the weeds. i was interested in finding out what it is

  3. Tom of Says:

    Marcus and George,

    Sounds to me like what you’ve found is the bryozoan Pectinatella magnifica. I assume you read my article on these blobs, but if not, you can find it here:

    What is this jelly-like blob under my dock

    The other commonly found blob-like things found in fresh water in North America are amphibian egg masses. But as you both are reporting these in mid-late August, that’s very unlikely. Most amphibians lay eggs in the spring. So I’m pretty sure what you’ve found is a bryozoan colony.

    Here’s another site with good info:


  4. Ask a » Jelly-like blob under the dock – part two Says:

    […] What is this jelly-like blob under my dock […]

  5. jack satkoski Says:

    I have noted these bryozoan colonies and have some good pictures if anyone interested.

  6. In Case You Were Wondering | Brandy Lake Muskoka Says:

    […] to North America and often grows on docks and other submerged wood.  Check of this simplified Ask A Naturalist web site..if you want more detail simply search the word. Click the site link to read the rest of […]

  7. Erinn Says:

    We found 4 of the jello nous blobs in lake simcoe

  8. Mark Dakin Says:

    I have some photos of very strange gelatinous blobs attached to submerged twigs and branches in the waterways near my home. I kayak a lot and see them everywhere but don’t know what they are. Is there a way for me to upload any of these photos for identification or can I attach them to an email? I’d appreciate the help, I’m very curious. They look almost alien. lol

  9. Tom of Says:

    Sure. Email them to Thanks.

  10. Mark Dakin Says:

    Thanks for quick response Tom! 😀 They’re on the way.

  11. Ask a » What are these green jelly blobs? Says:

    […] is “What is this blob I found in the water?” I’ve written about Bryozoan blobs and amphibian egg masses. Other possibilities for fresh water blobs include snail egg masses, […]

  12. Ask a » Donut blob that stumped the experts … Says:

    […] it wasn’t anything he’d seen before. I sent it to an expert on bryozoans, the “blob under my dock” that is one of the most common questions for The answer was negative. I […]

  13. Barb Says:

    I have also see “jelly-like blobs” in Stoney Lake. I have been told they may be algea. I have a photo if you tell me how I can post it.

  14. Tom of Says:


    You can email them to


  15. Sarah Says:

    Hello, I am a junior high science teacher and one of my students brought in a jelly like blob he took out of the Maumee River near Waterville, Ohio. The blob itself has algae growing on the outside of it, but is clear on the inside. It doesn’t appear to have any visible structures (individual sacs, cell membranes…) It really just looks like a lump of goo. Any suggestions? Thanks so much

  16. Brian Says:

    I’ve been seeing these gelatinous blobs for years in one local lake in particular. They are very strange both in appearance and texture. I’ve often thought that they must be some form of aquatic organism since I usually don’t start seeing them until late summer or early fall, and this article now confirms my suspicion. Thank you very much for the information!

  17. Tom of Says:

    I’m so sorry for the delay in responding. Did you by any chance take a photo? Late in the season, the bryozoan colonies drop the statoblasts, which are the darker colored structures that give the colony the speckled or polkadotted look. Once they do that, what’s left is a pretty clear blob. Which can then be colonized by algae and molds. That might be what you have.

  18. Paul Says:

    I’ve been seeing these for years growing on trees in a local lake that I fish. Curiosity finally got the better of my friend and I. I plucked one off a submerged tree near the surface, and set it on the boat to examine it. My friend also picked it up to take a look at it. About 5 minutes later we both had allergic reactions that looked and felt like Poison Oak going up our arms, the reactions lasted about 30 minutes and then went away. Interesting creatures, just be careful when handling them!

  19. Julia Says:

    Found dozens of them washed up on shore at Barren River Lake SP in KY after a rain storm on Halloween night. 2 were bigger than a football.

  20. Leah Cole Says:

    My husband and I saw many of these in Lake Grapevine in Texas. These are very strange. Thanks for the identification of them. Are they appearing in the lakes due to polluted water? Our lake even has aerorator over by our dam. I think they are gross and just wonder if those are growing what else is. And what do we need to do about it.

  21. Tom of Says:

    Leah, I can’t find a lot of information on bryozoans and water quality, but what I did come across suggested that bryozoans are associated with good water quality, not bad. Bryozoans filter algae and other microorganisms out of the water, so they would tend to make the water clearer, and some people have speculated that they can change the ecosystem by doing that. I find that a little hard to believe, unless there were a lot more of them than I’ve usually seen. So I don’t think you need to do anything about them. And their scientific name is Pectinatella magnifica, so you can think of them as “Magnificent Bryozoans.” Does that help change your image of them?

  22. cedelia obenshain Says:

    Hello! I picked up a piece of plastic that had been sitting out in the yard for about a year now. Under the plastic were two clumps of white squishy eggs. I felt so guilty that I had uncovered them, so I scooped them up in a handful of dirt and put them in an aquarium buried with moist soil. I want to know what they are and how to keep them alive! Please help me!

  23. avery born Says:

    I found one about 10 feet long under my dock on a rope

  24. Alan W. Says:

    Have Bryozoans on my boat lift tanks and hoses.
    Notice my lift comes up after I take the boat out. Would the broyozoans have air inside that could cause the lift to rise?

  25. Tom of Says:

    Hmmm …. interesting question. They don’t usually float at the surface, but that’s because they typically grow around a stick or rope in the water. I actually don’t know if they would be buoyant if they weren’t attached. Anyone?

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