We just got back from Coco Cay on the Monarch and I did see one small jellyfish while snorkeling. It was about the size of your palm. I overheard one guy say that one got him on the shoulder, but it was small so it didn't hurt too bad. More of a sting I guess. I steered clear. My husband was also snorkeling, but I don't think he saw any. There was some great snorkeling though. Lots of neat fish to be seen. We also saw a stingray on the far right of the beach just by the far right lifeguard stand in the sand.