1 Program RealTime predictions are based upon the historical outmigration pattern detected at a specific point, and its estimation accuracy therefore depends on regularity in these patterns. The annual patterns of fish passage over McNary Dam are influenced by a number of elements, such as the transportion of fish by barge around upriver dams (Lower Granite, Lower Monumental, and Little Goose Dams), the release of hatchery fish at various times in the season, etc. This is true of Rock Island Dam as well, where irregularities in the patterns of fish passage over Rock Island Dam occur largely due to hatchery releases upriver from the dam. These unpredictable events increase the variability of outmigration patterns from year to year, making accurate predictions more difficult and resulting in wider confidence intervals for the RealTime predictions.