Lots of stuff washes over the lower spillway steps. I am not sure what this is but the egret seems to feel it makes a nice perch.
Snowy Egret (Egretta thula)
snowy egretegretsmall egretwhite rock lakespillwayspillway stepsdallas texasaquatic birdaquaticwater fowlEgretta thulaoldrusted cartlower spillway stepswadersperchedrusty
From Aquatic Birds