Immature SNEG , actually. Originally I thought this bird to be immature LBHE. My observations were accurate, but not complete enough - (Pale yellow lores & bill base w/ gradual dark tip, green legs & feet, flashing wings to startle fish, about the same size as the nearby SNEG.) I have since relocated the bird and noted a few more things. The neck does not appear thicker nor the bill heavier at the base than the other SNEG's feeding nearby. The pale yellow lores were suspect. Its foraging behavior is similar to the other SNEG as is its general posture. Another photo (which I posted on eBird) that I was able to take today shows a distinct color change from green legs to yellow green feet, something I missed the day before. Also the leading edge of the legs show clear traces of black, which is something mentioned in Sibley for the juvenile SNEG. See the pic! (It was as if it knew what I came back to look for:)
Bill Schreitz