Incremental change can cause a collapse that is difficult to reverse.
What is particularly intriguing is the way that the lakes change. They exhibit what is known as hysteresis. That means you can “drip feed” them with fertiliser without causing much visible change until, suddenly, the whole system crashes and a new stable state, dominated by lake algae, emerges. To “uncrash” things it is not enough to push the lake’s chemistry back to where it was just before the flip. You have to go quite a long way past that point to bring back the clear-water ecosystem.
In order to preserve a system, you may have to take actions before things look bad — becuase the next incremental change could be the irreversible one.