Ivishak River Professional Review and Guide
"From headwaters on the north side of the Arctic Divide in the Philip Smith Mountains of the Brooks Range, the Ivishak flows north 95 miles to its confluence with the Sagavanirktok River. A large clearwater stream, the Ivishak begins in a narrow glaciated valley surrounded by peaks rising to almost 7,000 feet. Several of the small headwater streams that contribute to the Ivishak stem from relic Pleistocene glaciers hanging high in the valley. Porrupine Lake, east of the river in a glacial trough, is a natural reservoir for the upper river drainage.
The river begins as a single channel, and as it flows north, it braids and increases in size, taking on the Echooka and Saviukviayak rivers as major tributaries and coursing through a broad floodplain. Due to permafrost, water levels fluctuate daily, rising and falling dramatically with rainfall. Occasionally during dry spells in the Summer, parts of the river may disappear beneath the broad gravel channel. Shallow and swift, the upper 12 miles of the river drop more than 100 feet per mile. Below here, the gradient averages 32 feet per mile. Tributary streams have steep gradients. The stream collecting Porrupine Lake to the Ivishak has an average gradient of 167 feet per mile."