Well, sea water in the cove anyway. This was earlier this week.
The real story is the sand though - there is sand everywhere. This is the parking lot at work:
but it could have been anywhere around here.
It's put down in large quantities to provide some kind of grip on ice and packed snow - I make that sound like it doesn't work, but it's actually very effective. I guess it's cheaper than salt and probably works better when it's really cold. I actually remember this being a thing in my youth - I suppose it never went away in Maine.