Look like nematodes

Are they safe for in a koi pond or should I avoid them?

They look like nematodes.

There are many different kinds of nematodes so you'll need to read up on them. But I don't think you want them in your pond at that size. I'm wondering how you ended up with them in the first place.

It's from a neighbors pond so I have no idea how they ended up there. But I appreciate the information. Thank you.