A resting period for a nursery pond means that unwanted weeds, pests, and fish are all discouraged from developing a strong presence in the water. If a nursery pond is allowed to fully dry out and be exposed to sunlight, even further purification can occur. Sulfides and toxins from decaying organic matter are processed underneath exposure to open air and sunlight, removing buildup of chemicals within sludge and leftover water alike. Fry typically don't handle extreme cold or heat, meaning that nursery ponds may be left dormant in these months anyway. Seasonal nursery ponds allow for a 'refreshing' period between each stocking of new fish, this gives weeds and pests a chance to be cleared out, and reduces energy costs.