Natural swimming pools are filtered through aquatic plant growth and microbial action. Water in the swimming zone is pumped into a nearby regeneration zone. This zone is shallower than the swimming pool, and is filled with plants and aquatic life in order to filter the water passing through. Plants and bacteria eat the nutrients and waste found in the swimming zone, and allow clean water to flow back freely.
You'll want to use a skimmer or vacuum to account for larger debris that makes its way into the pool. A skimmer will get rid of floating waste, but a vacuum will reach deeper into the water to remove things from the floor or walls.
