Let us help you identify that mysterious object you’ve found.
Currently in CHALLENGE mode: If you've got something obscure knocking about, post a picture, and let's see how we do. Please prefix such posts with "CHALLENGE:" so we know we've got a fighting chance.
I'm not a biologist, but I found this on a google image search.
Pectinatella magnifica, the magnificent bryozoan, is a member of the Bryozoa phylum, in the order Plumatellida. It is a colony of organisms that bind together; these colonies can sometimes be 60 centimeters (2 feet) in diameter. These organisms can be found mostly in North America with some in Europe.
Didja poke it with a stick?
It's an invasive species that has been working its way west across North America. I hadn't heard of it in SoCal yet; this would be a drag. OP, what lake was it in? There may be rangers or similar authorities you could notify so they could look.
I wonder if OP can see replies to replies? I don't know how this works. What I'm saying is, I'm not OP.
I also recently found an invasive species of spider in my yard here in north San Diego, the false widow. Bummer.
I can see the replies 😀