Late afternoon is your best bet for rainbows over the rapids.

Yes, time of day matters — but direction matters more.

Rainbows form when the sun is low behind you and the mist is in front. For most river rapids (and especially from islands looking toward the main flow), the sun needs to be at your back and low in the sky — typically under 42 degrees elevation. That happens during the golden hours: early morning and late afternoon.

If the rapids or the misty section are to the east of your viewpoint, morning works (sun behind you from the west). If they