No mud should find its way into the swimming zone, as plants and the ecosystem are kept within the regeneration zone. The slimy bottoms of ponds and lakes are usually due to soil being allowed to flow into the pond, as well as a naturally clay bottom which allows plants and algae to grow in. Your swimming zone will have an impermeable liner, preventing water from escaping, or mud from entering.
If any sliminess does find its way to your swimming zone floor, consider investing in a vaccuum. This can remove debris and sludge from both the floor and the walls of your natural pool.
