Depending on the river an its depth, you will find lesser current the deeper it is. In moderate currents its like a drift dive but as Greg mentioned be prepared if you become separated from your buddy and know where the exit points are downstream from your entry. I would scout the river from where you plan on entering to where you plan on exiting and consider alternate exits in between in the event of an emergency. Also consider exit points beyond your planned exit in the event you cannot get out there Look to see if anyone in the area has dove the river or is familiar with it to get a heads up of hazards. Check out USGS website for stream flow data on whatever river you plan on diving. It will give you speed and gauge height and has reading from previous years. I would wait to the current is at its slowest before making a dive especially if you have little experience with it. Other than that enjoy and stay safe.