I don’t see this often, I think the first time was in the Harris Neck Stork rookery in Georgia. Snowy Egrets trolling for fish.
It looks like their version of the Reddish Egret, and Tricolored Herons fishing dance. Reddish and Tricolors are the masters though. They also use their spread wings as shade for the surface.
When the sunlight is harsh along the waters surface birds can’t see to grab small fish. They need to make the fish move.
This must be effective, all the small wading birds, as well as Black-necked Skimmers, try a similar trick.