The Hatchery dumps quite a bit of cold water out, keeping temps in the river pretty reasonable for trout fishing for a couple of miles. Expect more company the closer you are to the hatchery outflow.
My advice is stop a Hot Dog Johnnies for a late lunch, and fish anywhere upstream of there.
If you plan to fish the Big D for smallies, the glides by King Cole up to Washburns are easy to get to and wadeable. There will be fish everywhere, but they are more active as dark approaches. Below the boat launch in Belvedere is also good, but wading is a bit trickier, usually more luck with spinning gear there.