The tide is out
When the tide is out, you can walk to the forts on the other little islands. When the tide is in, you have to take a boat.
When the tide comes in it refreshes the water in that swimming pool you see. When the tide is out people can swim in the pool. We noticed huge tide rips in the water; it is probably unsafe to swim at low tide in the ocean - this is probably why they built the pool! Pretty neat!