Back in 1952, someone named William B. DeWitt, who may have been a parasitologist, wrote a paper about where he had found the snail Pomatiopsis lapidaria around Washington, D.C. Of the 3 locations he gave, all of which were along the Potomac River, one was a place he called "Fletcher's Boat House about two and one-half miles upstream from Key Bridge".
Early last week, when I re-read DeWitt's paper, it dawned on me that "Fletcher's Boat House" was the same place as Fletcher's Cove within the C&O Canal Park and which place I had passed by several times since last summer. There is indeed a boat house there for renting boats (not the house visible in the picture below).
Last Friday I visited Fletcher's Cove and after about a 20-minute search and after I had already written in my notebook, "No Pomatiopsis found", I found a live pair.
The larger snail was probably ~5 mm long.
Once I figured out where to look for them, it wasn't too difficult to find another pair; they must like to hang out in pairs.
So, almost 60 years and many floods later, Pomatiopsis lapidaria is still at Fletcher's Cove. I am planning trips to DeWitt's other 2 locations to look for the snails.
William B. DeWitt. 1952. Pomatiopsis lapidaria, its occurrence in the Washington, D. C. area and its laboratory rearing in comparison to that of Oncomelania spp. Journal of Parasitology, 38: 321-326.