Below Glen Canyon dam the Colorado River is unnaturally clear. Here, the turbid water of the Paria River enters the Colorado at the Paria Riffle, the first rapid in the Grand Canyon (actually, Marble Canyon here). The waters flow unmixed for some distance
The Paria's flows are so small at most times of the year that the added turbidity does little to return the large Colorado River to a natural state. Nevertheless, one can clearly imagine how turbidity alters periphyton growth and influences feeding by fish.