"a lake doesnt require water changes"
This is just not true. A lake, pond, sea, ocean gets major water changes and exchanges. In a lake, some water goes down into groundwater, some evaporates, other may run as runoff. Some lakes dry mostly, or substantially, in a seasonal basis. Then there is rain and meltdown and runoff that ends in the lake as well. Some have springs that lead into them.
This is just not true. A lake, pond, sea, ocean gets major water changes and exchanges. In a lake, some water goes down into groundwater, some evaporates, other may run as runoff. Some lakes dry mostly, or substantially, in a seasonal basis. Then there is rain and meltdown and runoff that ends in the lake as well. Some have springs that lead into them.