A variety of cased caddisfly larvae, probably mostly Neophylax, have clustered along the backside of a rock in fast water.  There seem to be some Helicopsychidae larvae clustered along the bottom, and a few other taxa are mixed in.  It's interesting that several larvae have especially large stones placed over the front openings of their cases, perhaps to block the case off for pupation.

It does seem to be the wrong time of year for Neophylax to be pupating, but that was the ID given for one of these which I collected and photographed up close.

From Cayuta Creek in New York