There are two entirely different kinds of streams flowing in the McCarthy-Kennicott area. McCarthy Creek and the Kennicott River represent one type; they draw much of their water from melting glacier ice and carry a large load of silt and glacial rock flour as suspended sediment. The other type consists of the clear-water streams originating from springs. Examples of these are Clear Creek, National Creek, Bonanza Creek and Jumbo Creek. These latter streams run clear the year around except during unusually heavy rains or the peak of spring snowmelt.
The glacial streams, like many in Alaska, are subject to erratic floods. Snow and ice melt peaks in July and turns such streams into raging torrents. The Kennicott River in addition is subjected to the annual outburst flood from glacier-dammed Hidden Creek Lake located along the west margin of the Kennicott Glacier ten miles upstream from the terminus. This outburst flood usually occurs sometime in July, resulting in exceptionally high water that at times can inundate the lower parking areas at the roadhead and cut off access to the bridge. McCarthy Creek, because it traverses the unstable landscape of a long valley downstream from its glacier, often carries a large load of non-glacial sediment. The head of McCarthy Creek valley is a convergence zone for precipitation that can generate destructive floods during periods of heavy rain.
Campers along both streams should make allowances for sudden and unpredictable rises in water level. The silt-laden waters are poorly suited for drinking, though they can be used in an emergency when collected in a container and given a chance for the coarser sediment to settle out. (Always boil or otherwise purify surface water before drinking.)
Owing to local geology, the clearwater streams carry "hard" water with a substantial dissolved mineral content that precipitates readily as scale in the bottom of teakettles. In fact, nearly all of the nearby clearwater streams cross private property and are regularly used by residents for domestic water supplies. For the benefit of all, please avoid camping near or polluting these streams. Some critical areas are posted against camping to help minimize contamination.