Good answer 7mm.
It seems to me that during the dry months, they make the water run in the dark. The trails are pretty easy to find. Sometimes you might see bucks heading back uphill to bed (after watering) in the first hour or so of light (while still in velvet). Once hard-horned, they pretty much just go "poof" - (gone), or are using alternate hidden routes that remain hidden to this observer.
With a river that close, you might want to examine any close by ravines or mucky rainstorm drainage areas that drain towards the river. Look for seeps or hidden water sources closer to bedding areas. Alder trees often grow in these wetter areas. It doesn't take much water to supplement their needs.