There are a couple of things of note to see at Deer Creek Bridge. The first is not all that obvious unless you know what to look for and where to look for it. We're looking upstream along the McKenzie River here, and the Deer Creek confluence is on the middle left side of the photo. The annotation below should help clarify why that's important.
During winter and spring runoff, Deer Creek makes an important contribution to the river, and Anne says you can often see a muddy plume here from its particulate sediment. At this time of year, it's a minor stream, and its particulate contribution is minor to effectively nil. Anne also pointed out that the Smith River, prior to being dammed (FlashEarth location) and diverted, entered the McKenzie mainstem above this point, but since the reservoir construction, it's not clear to me where the water from that pool re-enters the river.