Everything has been smooth going since opening the pool in April. All of a sudden today I noticed that the pool is losing a large amount of water. I went out to where the hose for the pump releases the water (when backwashing, etc.) and had a small pond in my yard.

I checked the pump to make sure it was set on Filter, and it was. Why is it pulling water from the pool? Is something wrong with my pump?
Sorry to sound like an idiot but this is my first pool. Hopefully someone will have advice for me. Thanks!