To know what "part of a lake" does not seem very important. A different variant would be found in an area where there was some deterrent to separate fish. In a lake, the fish just swim across the lake, it is not like they are bound by a separate river or a separate lake completely. I think fish from any particular lake will be uniform. That is kind of like needing the exact coordinates your fish was collected at, mine was collected 100 feet further east, there would be no difference.