The following links give stream flows for many rivers in Colorado. This information can be especially important during runoff season, from April into July, and for tailwaters, where water managers control the flow year-round. Keep a journal or call local fly shops to get an idea of what a fishable or unfishable flow is for a particular river.
Colorado Current (Realtime) Stream Flows – USGS
Provides stream flow for previous week in addition to latest flows.
Colorado Division of Water Resources Surface Water Conditions
Current stream flows at more stations than are available through the USGS site.