@ljellis tweeted that the plant misidentified in my photo as “cattails” might be “Harding grass,” or halaris aquatica. Looks and sounds reasonable to me from the description I read online as to the form of the plant and where it grows.

The disappointment is that it is described as an “invasive species” – that can’t be good! But, darn, I still like the photo. If anyone else has further info on this, or a confirmation of the identify of the plant, I’d welcome hearing from you.