[en] Idaho Supplementation Studies (ISS) will help determine the utility of supplementation as a potential recovery tool for decimated stocks of spring and summer chinook salmon, Oncorhynchus tshawytscha, in Idaho as part of a program to protect, mitigate, and enhance fish and wildlife affected by the development and operation of hydroelectric power plants on the Columbia River. The objectives are to: (1) monitor and evaluate the effects of supplementation on presmolt and smolt numbers and spawning escapements of naturally produced salmon; (2) monitor and evaluate changes in natural productivity and genetic composition of target and adjacent populations following supplementation; and (3) determine which supplementation strategies provide the quickest and highest response in natural production without adverse effects on productivity. Field work began in 1991 with the collection of baseline data from treatment and some control streams. Full implementation began in 1992 with baseline data collection on treatment and control streams and releases of supplementation fish into several treatment streams. Field methods included snorkeling to estimate chinook salmon parr populations, PIT tagging summer parr to estimate parr-to-smolt survival, multiple redd counts to estimate spawning escapement and collect carcass information. Screw traps were used to trap and PIT tag outmigrating chinook salmon during the spring and fall outmigration. Weirs were used to trap and enumerate returning adult salmon in select drainages