In ground swimming pool areas with high water tables and heavy rain events, the water pressure under the pool can actually cause the liner to float.
When this occurs, the liner looks like it’s actually inflated, and feels like a water bed when walking on it. You can also see wrinkles in the floor that were not there before on small events.
In most cases this incident does not damage the liner, but it normally results in wrinkles in the liner after the ground water recedes and the liner falls back into place.
To fix the ground water issue
Install a dewatering system around the pool that will keep the ground water around the pool to a minimum.
This will obviously keep the liner from floating again.
To remove the wrinkles in the liner
Drain the pool and re-set the liner if possible.
But this is a slippery slope. If the groundwater is still there, this will turn into a big mess. Liners can also be damaged and not be repairable in the reset process.
It should also be stated that liners more than 3 or 4 years old dry, shrink, and become rigid VERY QUICKLY. So I would not recommend this process to anyone without experience working with vinyl liners.