Water shoes are nylon topped (stretchy) shoes with rubber bottoms. They are light, fast drying and protect your feet from coral, shells or rocks in the water. They are also great for walking on the beach. Cheap versions can usually be purchased in spring and summer at Wal mart type stores for $5 to $10. Same goes for Teva type sandals. Cheap versions can be purchased same places as the water shoes, better sandals (tevas) at shoe departments in major department stores and major sports chains.
The sandals are good for summer time hiking as well as around the water.
I recently purchased an upscale water shoe from Lands End and wore them everywhere in the water and on the ship on a Windjammer cruise. They were perfect (for me).