Part of a HUGE infestation; there were several patches on “islands” in the middle of the creek, and very dense patches along the creek bank. Zoomed out shots show the extent of the largest dense patch; it covers more than an acre of land easily.

Visiting as follow up to reports by @inarticulate. Can confirm all their notes. Also, these photos would look even worse but someone cut the tops of hundreds of plants off, pulled many, too. I would estimate that there are many thousands of fumeworts here. A very tiny percentage of the seed pods have started to explode when touched.
In the 2nd photo you can see the bluebells and the area between the bluebells. That stuff in between the bluebells is mostly incised fumewort.
Post script: I've added two more photos and arranged them to show the walk down an ~50 ft long side-path immediately upstream of dam. #1: At entrance to the path, the native spring ephemerals, mostly bluebells, look fine and there's no noticeable fumewort. #2: A few feet further and you can see individual fumeworts among the native spring ephemerals. #3 #4: At the end of the path large percentages of bluebells/natives are being displaced. All that area in between the bluebells is fumewort. It would be easier to see in the photo but a volunteer (whom I had not met yet) had cut the tops off all the fumeworts!