Hi bobad,
No, it is not new. It is 30 years old and average depth is about 8ft. Right now it's actually deeper than that since I measured it last year in the dry season. I was going to do another set of measurements to see how deep it is when it is swollen. I also have no overflow outlet. I'm guessing that when it did fill it was rain water. We just bought this place in fall of 2005 and it was the same then as it is now.