It’s a little blurry but it looks like there is a distinct head capsule on the upper left end which would make this a larvae, rather than a worm, which can be pretty common in pond water depending on your region.
How big are the larvae? Maybe too big for their mouths? Will be interesting to see what they turn into.
Check this identifying site out and maybe you can figure it out. https://entomology.ca.uky.edu/ef017
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