I've only spotted this single one Bittersweet nightshade, Solanum dulcamara, around the lake. Notice how the leaves each have two little wing-like leaves. Of course, with flowers like these, just how much more does one need to make an ID?
I'll be looking for more of these plants and trying to get more shots of this one. The day I got this shot, it was terribly windy on the far end of the lake. It is so hard to focus macro shots with even the slightest breeze. I'm looking forward to some of those hot, still days of summer.