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While satellite data indicate that the surface expression of the North Pacific marine heatwave, nicknamed "The Blob," disappeared in late 2016, Argo float and ship-based conductivity-temperature-depth data show that warm conditions persisted below the surface mixed layer through at least March 2018. We trace this anomalously warm subsurface water from the open ocean through Queen Charlotte Sound to Rivers Inlet, on British Columbia's central coast. In Rivers Inlet, deep water below the sill depth continues to be 0.3 degrees to 0.6 degrees C warmer than the monthly average, suggesting that impacts of this marine heatwave have persisted in coastal waters at least 4 years after its onset, with potentially substantial effects on coastal ecosystems.

Plain Language Summary The Northeast Pacific Ocean was affected by two warm water events, the first was the 2013 to 2015 marine heatwave, nicknamed The Blob, and the second was the 2015 to 2016 El Nino. Surface satellite data have shown that the warm water was gone by 2016. Using temperature data collected by ship and by autonomous robots, we find that abnormally warm water continues to exist in the open ocean below the surface, at about 140-m depth. In the coastal ocean, we find that deep waters in Rivers Inlet are still 0.3 degrees to 0.6 degrees C warmer than normal, at least 4 years after The Blob was first observed. This warm water could have a big impact on the Rivers Inlet ecosystem.