Here in northern Colo you can collect from the local streams and pond areas. These are public areas. Stay out of private property areas that are posted. I've collected in these areas in the past, but my luck has been minimal. The problem being, it's very difficult to duplicate the environment of the area where you collect. It's been my experience that the local plants and fish have a very short lifespan in a fish tank.
"Fear not, my young apprentice. Just change the tank water."