Cow Moose Feeding on Marine Plants

Cow Moose eating underwater plants at remote lake near Prince George B.C. She is 500 meters across lake from us so can't see us but can hear the waves slapping the boat. We can't see her either except through the viewfinder. Camera Canon L1 with 600MM telephoto lens and one 2X extender giving total of 1200MM. Two tripods we are using is still not enough to keep camera perfectly steady.