If I am only going to Arena, I will use the empty canoe to cruise, fish, and explore before packing to head down river. Trees in the middle of the river are a sign of shallow water but you need to be careful because fast currents can be created by the obstructions. . Gusty winds and dark clouds are a sign that things could get exciting. Six inch waves near the shore indicate that waves in the middle of the river could be 1 foot or more, plenty high to capsize a canoe. If the waves pick up, keep the bow of the canoe pointing into them and head for calmer water nearer shore.
Thunderstorms are always possible in the summer.
Strong gusts of wind can howl down or across the river. Lightning and thunder can be part of the show. Look for an island that has cover to block the wind and get off the river. Pull the canoe well off the water. Remember the river can rise several feet as a result of a strong rain in the river's watershed or from the opening of the dam flood gates up river.