You can always tell when the tide is moving, and schools of fish are around it.
There is action above and below the water. A simple signal are the big Pelicans.
They move with the Dolphin below and the small terns making quick dives.
In open water the Pelicans dive for fish, but when inside shallow inlets they can sit on the shore and make quick grabs of the smaller fish. When a Dolphin herds fish these guys will crash right in with the huge animals a steal from them.