My uncle’s cabin on the Susquehanna River has a rock formation a hundred yards off shore: a low, stacked rock dam with a channel in the middle. As kids we would stand in the channel with minnow nets. Now I learn it was possibly a Native American eel weir (though the eel population is now only a small fraction of what it was prior to the 1950s). It doesn't quite have the classic V-shape, but looks like it may have been a partially natural formation that was then modified.

https://www.bayjournal.com/news/fisheries/dozens-of-ancient-...