I think I'm about to dump this set up. Camera doesn't seem to want to focus properly even in pretty large birds. Almost seems as if 200mm is as much as things can handle.
Everything with the Sigma 150-600 was just trash no matter what I did, even off a tripod at over 1/1000 sec with is turned off and one shot. Time to walk away from the lens for a while... 
Anyway, switched to the canon 70-200 f/2.8L is ii and managed to get a little something, a coot I believe...
Actually I kinda like the texture and colors of the water here 
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