The river can be paddled from approximately 300-800 cfs. At the lower limit of flows the run is a technical creek and at the higher limit of flows some of the holes can pack a punch. While there is no gauge on the Cooper you can estimate flow in a couple ways. First, the Cooper is a tributary of the Cle Elum. Discharge of the Cle Elum upstream of the reservoir is calculated from change in reservoir height and release from the reservoir. The value can be found on the USBR Yakima Project site as reservoir inflow for the Cle Elum (keep in mind this is a caculated value and sometimes the numbers are a bit off). Looks for flows of about 800 to 1200 cfs although lower or higher flows are possible. To see data from the last few days go to the data archive, select station CLE with parameter QU which is the calculated inflow. For a second check, the Teanaway River at Forks is maintained by USBR and is the next drainage to the east which can give you an indication of flows in the area. Look for flows around 70 cfs on this gauge after the spring snowmelt. At higher flows this run is class V and more continuous. At lower flows it becomes mostly IV+ with a couple of drops in the V- range.