Final answer:
Buoys with even numbers should be to the right when proceeding downstream due to the navigation rule resembling 'red, right, returning'. This is related to the general boating practices for conserving energy and making navigation easier by utilizing the flow of the current.
Step-by-step explanation:
When canoeing, buoys marked with even numbers should be kept on your starboard (right) side when proceeding downstream. The reasoning behind this is based on the "red, right, returning" rule, which is a navigation rule indicating that the red buoys are to be kept on the right side when returning from the sea or heading upstream. Conversely, when heading downstream, you would keep the even-numbered green buoys on your right. In fast-moving waters, traveling near the middle of the stream when going downstream can be advantageous because the current is typically stronger in the center, which can help propel the canoe along with less effort. In contrast, paddling upstream is generally easier near the shore where the water flows more slowly and the paddler can avoid the faster current.