Nothing beats a dip in the pool on a hot summer day to cool you off and leave you feeling refreshed. If you have an above-ground inflatable pool, you must deflate the pool and pack it away when cooler weather arrives. You may also want to remove a noninflatable above-ground pool. If you originally set up your swimming pool on a grassy surface instead of a deck or patio, you will likely notice an unpleasant odor emanating from beneath your pool when you remove it.
The bad odor you smell after removing your pool is characteristic of decaying organic matter. All grasses need sunlight to survive. The University of Florida notes that even "shade" grasses require some direct sunlight throughout the day to survive. The grass directly beneath a heavy object, such as an swimming pool filled with water, receives none. Eventually, the grass beneath the pool dies and begins to decay. When you remove the pool, the odor becomes apparent.
Decomposing matter gives off a rotting odor as bacteria break down the material. Although the odor decomposing plants give off is generally not as powerful as that of decomposing animals, it's still unpleasant. According to Washington State University, the presence of oxygen notably lessens the foul odor associated with decomposition; introducing oxygen to the rotting plants reduces the smell. A swimming pool not only blocks the grass from receiving sunlight, but also blocks a considerable amount of oxygen -- intensifying the odor the rotting grass gives off when you remove the pool.
While the decomposing grass beneath your pool gives off an unpleasant smell, you may have another odorous culprit lurking within the dead grass -- mold. If any mold spores were present in the grass when you installed the pool, these mold spores need only food, moisture and the right temperature to grow rapidly. All these factors are present beneath your pool during the summer. The musty odor of mold coupled with the smell of decomposing organic matter makes for quite a stench when you remove the pool.
The bottom of your pool remained in contact with the decaying grass for a long time and may have absorbed some of the foul odor. Before you store your pool for the winter, clean the bottom of the pool as well as possible with water and a mild soap. Avoid using harsh cleaners that could eat a hole in the pool's vinyl. Dry the pool in the sun. If cleaning and sun-drying the pool does not rid it of the foul smell, scrub the bottom of the pool with a soft-bristled brush dipped in warm water mixed with either baking soda or vinegar.
While you cannot stop the grass underneath your pool from dying, you can reduce the odor the decomposing grass gives off by spreading sand over the area where you plan to set up the pool. The sand absorbs the odors beneath -- making the smell less offensive the next time you remove the pool. If you have a ground-level deck or patio large enough for your pool, consider setting up the pool there to avoid the bad odor altogether.