Is This Pennywort?

It blew in against my dock and appears to be dying off?

Yep.

Very easy to kill, but will probably need multiple treatments if it's rooted. Post treatment peripheral popups are not uncommon.

Pennywort

EDIT: Tbar, can you take some pics of the shoreline plant in the top right corner of the first pic? It's hard to tell, but it looks like waterleaf. If so, you don't want that.

Waterleaf

Regret no I don't have a close up of that area.

I have not had much vegetation(except bull rush)the last couple of years so I am glad to have something.