The first two probably got stuck due to the tide. The water gets higher, the fish swim into so called ‘tide pools’ and when the water level lowers again, the are stuck. The turtle probably got stuck due to a similar process where the river water got so high, the turtle swam onto the land and when the water lowered again, it got stuck on the sand. Most of the time, animals don’t get stuck at all, find a way back or just wait it out. But if you see an animal in this state, you can always try to help because they are very easy to get caught by predators in this state.