South Boulder Creek or SBC as the local call it is one of the closest tailwaters  you can fish in the front range.  The upper section has some public access above gross reservoir, but most of it is private leaving the most popular section, the tailwater as the likely destination.  Below Gross, the river is fishable year round as long as the flows stay up.  The state drops the flows below 25cfs often in the winter creating fish kills and iced rivers, but if they keep the flows going year round, the fishery is quite excellent.  Mainly rainbows and browns are caught in the tailwater section as well as down into town.  Up above you can catch brook and cutties.  The river is a great place to spend a day or half day since it is so close to access and requires little effort to reach.