Generally aerobic decomposition is considered good composting and anaerobic bad. If you are composting in a composting bin, probably water logged, O2 deficient zone of compost smells rotten and that’s why they say this, but in nature there are both aerobic and anaerobic decomposition occurring at proper places.
If you make a small pond and put some plants and fish, and don’t forget to feed these things. Soon you might start smelling some bad odor so you change water and put some clean water from tap. Chlorine treated and clean…. some days later same thing happens. Water is rotting.
Some naturally occurring ponds. Nobody changes water, but there are fish and ducks and some water plants… and amazingly no foul odor.
This Pond No Rot
So I took another experiment. This time using plastic liner pond which holds about 50 gallons of water. I didn’t want soil to be natural filter and colony of bacteria and also I kept procrastinating so this was a quick way to do it. I pour water, not tap water. Chlorine kills bacteria both good and bad. Isn’t that the purpose?