Water Hemlock

I wouldn't rule out the hemlock. It is a water loving plant. Wild carrot prefers dry fields and waste places. Do you have closer views of the leaves, stems and blooms of this plant or full image of the whole plant? It looks quite large for wild carrot and I think the blooms look slightly different shaped. Wild carrot has delicate, fern-like leaves that smell like carrot when crushed. https://plants.usda.gov/java/largeImage?imageID=daca6_007_ahp.jpg Here is a plant I found (Cicuta maculata): http://www.projectnoah.org/spottings/122796013 This was found growing in a local park, right by the water. It was a very tall plant. Note how the plant branches. Take a look and see what you think.

Also Angelica and lovage have a similar look. Too narrow it down, you could use a key to the genera of the carrot family and think about details you can remember -- was the plant hairy? Were the stems hollow? Etc.

There are a lot of plants that look like this, hmm... Queen Anne's lace, cow parsnip, poison hemlock, water hemlock?