I also battle honey locust trees on my property! (Make sure you poison the stumps correctly, or you will get massive resprouts, and perhaps some root nodes away from the stumps that also pop up new trees.)

I have not put any branches in my ponds, just because they are a pain to transport. I try to burn them in place.

I believe one member did put some in his shallow water to provide refuge for his forage fish. He did not ever report any problems with that.

I think your fish should be fine with those evil looking thorns in the pond. If you make the cover pretty dense, it should be good for your small forage fish. Maybe a predator fish might get stabbed if he makes a mad charge into the cover trying to catch a meal, but I can't imagine that would happen often.

Do you have a weed burner? If not, they are pretty cheap. You might try making a few quick passes over your thorns when your locust are freshly cut. I think you may "wilt" the sharp tips if they are mostly green. (The hardened ones might be unaffected, or need extra fire time if they are drying out.) That may make the wood easier to move for you.

Are you moving by hand, or with grapple and skidsteer? If moving by tractor and FEL, be VERY protective of your tires!