Freshwater something

A warm day here, so I took the dog for a walk at a park on the lake not far from me...usually a fishing spot for boaters to put in the water..no one was there which was nice..no leash on the dog!   The lake has been pulled down for some work reason which left the shoreline full of tiny shells.  In all the black, gray and white, this tiny shell that was aqua/teal color just jumped right out at me.