The term 'River Idaho' can be solved by the crossword solution 'SNAKE' which is a five letter word. The SNAKE River is a major river in the northwestern United States, located in Idaho. It is the largest tributary of the Columbia River, which it joins at the Tri-Cities in Washington. The SNAKE River is 1, 078 miles long and is the second longest river in the United States. It is an important source of irrigation water for the region and provides habitat for many species of fish and wildlife.