For a real urban experience, try Caltech in Pasadena. There used to be long, rectangular raised cement ponds as part of the university landscaping. Along with lily pads and goldfish there were absolutely huge bullfrogs (bigger than a softball)and large crawdads. I assume they still exist. This was 7-8 years ago when my kids would use bacon on a string to catch and release the crawdads. Of course, the campus guards told us to stop. But they're fun to look at.