Assessing a river's depth can be challenging, but looking at the rocks, waves, and water flow can help indicate depth. NPS / Jeff Shearer. Glacial rivers are often easier to cross in the early morning when the temperature is cool. NPS / J. Mills. Assess the Water's Properties. Toss a stick in up stream to get a feel for the water's speed: the swifter the water the shallower it has to be to cross safely. If you cannot walk as fast the the stick is floating downstream, it is probably not a safe spot to cross.