Cow-nosed Ray

This past weekend we had a Labor Day party and had an uninvited guest. Not that we were too upset by their appearance.
We had walked out to the end of our pier and were standing around talking while the kids used colored chalk to mark every nail on the pier. Then suddenly several of us saw a fin appear out of the creek. The water was mid-tide rising and has been running a little on the high side all week. The creek is always very muddy so all we could see was the exposed fin; nothing below water. There were a few more sighting over the next couple of minutes.
The only reasonable identification would be a cow-nosed ray. The creek is too shallow for a dolphin and probably too shallow for the sharks found in the bay. Plus, the fin seemed to come up from the side and back down instead of arising straight out of the water.
This is the first ray that we have seen from our pier. I did some a few several years ago while kayaking closer to the bay. They were moving around in shallow water behind Grandview Nature Preserve. At first we thought they must be dolphins, not realizing how come the rays are, but some investigating afterwards convinced us that they were rays. Not least of all was the fact that we always saw two fins come up together. That definitely seemed like feeding behavior.