There is a legend that there is a tortoise under the shadow pool. The fish in the shadowless pool are under his control. This seems to be more than just a legend, at intervals when the shadowless pool releases water. The big fish in the shadowless pool are gone. But there are filters in the outlet when the water is released. Some people also claim to have seen the tortoise, but there has been no definite evidence. Perhaps in the near future, this mystery can be solved by the world.