If you were growing a population in a laboratory under optimum conditions, the growth would be rapid. This same thing occurs in nature. If you leave one dandelion growing in the yard, soon you will have many of them. As long as the seeds are being made, other plants will grow. Until humans or predators intervene, this explosion continues.
Sunlight affects plant growth in lakes as well as on land.
Suppose runoff water contains large amounts of fertilizer. This makes plants in a pond grow. They soon become crowded and deprived of nutrients and die. This produces carbon dioxide among other nutrients and takes oxygen away from fish. Soon there is not enough oxygen produced for fish and they die.