Today was our first swim day and I noticed that at the deep end of our fiberglass pool there is a spot about 3 feet in diameter that seems to have sunk in. It's like a sink hole. I would say it's about 4 to 6 inches in depth. It was definitely not there last summer. We do have a lot of ground water in the wet months. Our drywell stays pretty full during this months. In the summer thought, it stays dry for the most part. Is this a major concern? The side walls are fine--no bulges.