Juvenile steelhead (Oncorhynchus mykiss) enter the northern California Current ecosystem from the Columbia River and other Northwest coastal rivers and include several populations listed under the US Endangered Species Act.  However, relatively little is known about the response of these populations to interannual variability in ocean conditions.  In 2015 and 2016, anomalous ocean conditions, called the warm ¿Blob¿, persisted in the northern California Current, increasing ocean temperatures by >2.5°C.  To determine how steelhead respond to such major shifts in temperature, we compared juvenile steelhead diet composition, stomach fullness, size, and body condition across a 16 year time-series (2001-2016). This time-series included both the Blob-influenced years as well as other warm, cold, and average temperature years.  In addition, we used bioenergetics models to assess the importance of the marine environment in contributing to changes in steelhead condition under different ocean temperature scenarios.  Steelhead from 2015 and 2016 exhibited some of the poorest body conditions but were the largest sizes in the time-series.  In contrast, steelhead caught in 2010, an El Niño-influenced warm year, exhibited unusually high body condition and stomach fullness, but were generally quite small.  Steelhead diet composition varied between warm and cold years and between warm and average years, with steelhead consuming more insects, juvenile rockfishes, and rare and unidentified fish in warm years. Unusual taxa such as gelatinous salps (both years) and juvenile smelts (2016 only) were consumed during this warm period.  Bioenergetics models indicated that interannual variability in growth is influenced by changes in temperature and feeding conditions in the marine environment. Significant differences in growth between warm and cold ocean years became apparent by day two of the simulated marine residence. These findings highlight the potential for warm ocean years to influence the diet composition and morphology of declining Columbia River steelhead populations and may lead to a better understanding of factors influencing survival of juvenile steelhead in the early marine residence.