Another boat we encountered seemed to be weaving all across in front of us, and zigzagging, not taking the usual clear evasive action when meeting another boat. We wondered if they planned to pass on the non standard side (and if so why) or if the steering wheel was with a new driver who was overcompensating for a slow response compared to a car wheel. There was plenty of time and space to sort out and as they passed us, on the correct side, someone shouted that the river had shallow spots that they were steering around just there. Shane speculated that they had sonar as there were no buoys warning of shallow areas or underwater hazards, which are often well marked.