Final answer:
Paddle near the shore when going upstream due to weaker currents, and in the middle of the river downstream to take advantage of stronger currents.
Step-by-step explanation:
When paddling a canoe upstream, it is advised to stay near the shore because water currents are weaker due to friction and resistance from the shoreline and obstacles. This causes less force to be exerted against the canoe, making it easier to paddle and navigate upstream.
Conversely, when canoeing downstream, the middle of the river is preferred since the water currents are stronger there, providing a natural boost to the canoe's velocity. This assists with traveling downstream, making the journey less labor-intensive.
Paddle near the shore when going upstream due to weaker currents, and in the middle of the river downstream to take advantage of stronger currents.