I've only snorkeled in Hawaii, but when I sold off my cold-water gear I did keep mask/snorkel/fins/weights. My plan is to try snorkeling here locally, using my kayak fishing drysuit. I can't take the weight of tanks and such anymore, but i still want to have my play time...
I've seen some fascinating Youtubes of river snorkeling
And snorkeling for flounder would be fun, I bet.