From seated in a rowing shell: Potamogeton nodosus. My plant biologist friend will probably label this as an “infructescence” (a cluster of fruits).
Feeling mildly guilted by @marlboromaam, I managed to ID this plant myself before submitting this to my plant expert. It's always embarrassing to learn that it's something that's been ID’ed for me before and I photographed this plant at the lake 5+ years ago.
Retired economics professor (“dismal scientist”). Married 40+ years to the love of my life; we have two grown daughters, both married, two granddaughters and a...