Well, not so much the color of the river per se, but it was the color along the river last week in Wisconsin and Michigan during the peak of the fall color show that was impressive. Some examples, seen between rain showers:
We know that warm days and cool nights of fall stimulate plants to break down their chlorophyll, unmasking all the xanthophyll and carotene photo pigments in the leaves, and those changes in leaf metabolism produce the yellow, orange, and red colors. I have written more about the chemistry of leaf color change earlier — (“you know it’s fall when…”). But what accounts for the synchronous color changes of rural northern hardwood forests, compared to the more prolonged sequential color changes we see in urban landscapes?
Lots of factors might be responsible: urban areas are generally warmer with a less homogeneous climate than surrounding open countryside; plants in a natural forest most likely respond to climatic changes in similar ways, whereas planted urban trees, often non-native, adapt to a mixture of environmental cues with different schedules for leaf fall. Leaves might change color more slowly and stay on trees longer in the urban environment simply because temperature and moisture conditions there are so different from the surrounding countryside.