I photographed this bird there last spring. I believe it's a Great Egret.
CORRECTION: I originally posted this as "Snowy Egret," which is what a friend told me it was. However, the Cornell's All About Birds indicates that the Snowy Egret has a black beak and yellow feet, whereas the Great Egret has a yellow beak and black legs and feet. Since there is already a reference to this post on another blog, I thought I should put in this correction.