Wildlife Spotting

This plant looked very much like poison hemlock, except the leaves were much bigger and the stems lacked purple streaks. There may have been some subtle reddish hues on the stems near the base, and at the edges of the leaves. Each specimen was growing with the base submerged, so it was definitely a water loving plant, forming dense thickets. Hogweed? Angelica? Water hemlock? Not sure, but curious to know.
Edit: may be pacific water parsley, or pacific hemlock parsley. Those seem to have the right leaf size, anyway -- the leaves of angelica and hogweed are too big.