This is what our pool looked like 8 years ago when we moved in. It had bullfrogs living in it. Everyone told us to just fill it in. I spent an entire week hauling buckets of sludge out of the bottom of it that I dispersed around newly planted privacy trees. It was a nightmare.
I'm glad we didn't. I was keeping maintenance under 500$ a year, but with the price of chlorine, I'll blow past that this summer easily. Still, glad we didn't just fill it in.