Back in 2006 while on vacation, I saw two Sandhills in a field along that highway that runs East-West just South of Jackson, Wy.
They were unmistakable to any other bird due to their stature and characteristics. I not sure that a Sandhill would persch on a stick in the middle of a lake. If they were there, they would more likely be strolling along the shoreline in the tall grass. At a distance, one would almost think that they are small man. Their appearance is that big or at least the two I saw were.
A Whooping Crane would even be bigger. They do breed in Canada and winter on the Gulf Coast and I suppose could come into your area.
I suspect that by your description of its habit on the lake that it is a large heron. There are color variants of the Great Blue.
I usually don't use the WhatABird Guide due to sometimes the painted pictures are not the clearest representation of the colors that you see in the wild. The colors are more subdued or otherwised affected by lighting conditions. However, the member's picture Galleries are very useful.
If you do not have a Bird Guide, then go Online and do some queries of several likely birds and see if that helps.
Good Luck.
http://whatbird.com/forums/photos/birdman/
