Ponds go through cycles or periods where they are either growing beneficial bacteria or they're not. It's evident when they're not growing microbes because you will see and increase in algae and sediment accumulating in the pond. Most would see the increase in sludge and determine that the pond needs a thorough cleaning and may be inclined to drain the pond. If constructed correctly and given the chance, natural occurring microbes will digest the sludge and actually clean the pond.
