The Tide is a Thief

When my family and I went to the beach, I went and bought this killer bikini and sandals. They matched perfectly, and they were rather expensive, I had to save up for them. I made the mistake of wearing them to the beach when we went and walked with them in the water. They said they were waterproof, but it never said they were slip proof. One of them came off after it got stuck in the sand and then, in a matter of seconds, it was out in the ocean. I tried so hard to get it back, to no avail. I almost cried, but I've always kept the other sandal (too expensive to just throw out) wondering who might have the other one, if anyone does.