You need to choose a place with many fish. When you put a cage, you need to have a certain understanding of the environment. Generally, it should not be placed in shallow water, but it should not be too deep. If you want to avoid water plants, you can be near them.
It needs to be placed upstream of the water. Generally, reservoirs are closed, but there is always some river water flowing in. It needs to be placed at the place where rivers and reservoirs flow in and at the bottom of the reservoir.