I'm glad its not a flux magnifier since I'd not be wanting a tingling in the buttocks when its being repaired. Its a (broken at one end) floating boom to keep rubbish out of the Swan Drawdock. Should be doing its job again soon.
This looks like part of a flux magnifier from an alien spacecraft that broke up upon entry into the earth's atmosphere. (No relation---I hope---to Flux, Utah, USA.) Did you feel a tingling in your buttocks while taking this picture?