Why can clear water from the Great Bear River be seen separately from Mackenzie River water?

The clear water from the Great Bear River remains distinct from the Mackenzie River because of a clear summer demarcation between the two bodies of water. When the Great Bear River empties into the Mackenzie at the village of Fort Norman, the Mackenzie is characterized by its silt-laden water, while the Great Bear River contributes cold, clear water. This contrast in physical properties is so pronounced that the two flows remain visibly separate along the eastern bank of the Mackenzie for approximately 50 miles (80 km) northward.1