Spring 2006 Gas Bubble Trauma Observed in Fish – Preliminary Analysis

Jan 25, 2026

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This report examines the incidence of Gas Bubble Trauma (GBT) in fish sampled during the spring migration at multiple dams, including Lower Granite, Little Goose, Lower Monumental, McNary, Bonneville, and Rock Island. Over 9,000 fish were analyzed, revealing that at tailrace Total Dissolved Gas (TDG) levels near 120%, the incidence of GBT in migrating salmonids remained minimal. However, operational limitations at Lower Granite Dam resulted in increased TDG levels, negatively impacting fish over extended periods. Management practices also contributed to elevated GBT levels in migrating salmonids.

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Spring 2006 Gas Bubble Trauma Observed in Fish – Preliminary Analysis

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Spring 2006 Gas Bubble Trauma Observed in Fish – Preliminary Analysis Margaret J. Filardo
Fish were sampled at Lower Granite, Little Goose, Lower Monumental, McNary, Bonneville and Rock Island Dams. • Over 9000 fish were examined for GBT during the spring migration season. • COE Waiver Conditions for GBT are 15% of fish showing signs of GBT in non-paired fins.

Summary • At tailrace TDG levels near 120% the incidence of GBT in migrating salmonids was minimal. • Project operations limitations at Lower Granite Dam resulted in higher TDG levels that showed effects of GBT in fish over long periods of time. • Operations for management of excess market spill resulted in elevated levels of GBT in migrating salmonids.