I don't get a chance to submit to challenges much since I do wildlife photography but I do have this cattail shot. Taken with Canon 1DX2 and 600/4 IS II 1/100 F8 ISO 100. I was set up waiting for a bird to land on this cattail thinking it would look good, they were flying and landing all around just never on this spot.
Definitely not at the level of others, but maybe the only shot submitted at 600mm.