Fall is nearly here and, for most of us, that means the end of the summer heatwave. In the waters of British Columbia, however, the seasonal cycle is stuck. A marine heatwave began more than four years ago and new research suggests it won’t be disappearing anytime soon.

Marine heatwaves are not new. But heatwaves are getting more intense and more frequent with a changing climate. Over the fall and winter of 2013 and 2014, satellites detected above normal temperatures in the surface waters of the northeast Pacific. At its peak, the mass of warm water—nicknamed “The Blob”—had water temperatures up to 3 degrees Celsius warmer than normal and covered an area larger than Australia.

Scientists repeatedly thought the marine heatwave was abating when satellite observations of sea surface temperatures moderated after winter storms. But satellites cannot measure temperatures below the surface.

“[The new] work highlights that you cannot effectively monitor the ocean with just satellites,” says Jennifer Jackson, an oceanographer with the Hakai Institute.

Jackson and colleagues showed what satellites missed—that substantial heat remains at depth.

Jackson and colleagues Greg Johnson (NOAA Pacific Marine Environmental Lab), Hayley Dosser (University of British Columbia), and Tetjana Ross (Fisheries and Oceans Canada) combined four separate time series from oceanographic monitoring programs along the coast of British Columbia. The collaborative group noticed strong similarities between data sets from the open ocean and the coastal fjords of British Columbia.

“By combining diverse data sets you are able to describe the progression of this subsurface warmth from the ocean onto the coast and into the fjord,” says Johnson. “I think that’s pretty cool.”

Recently accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union, the time series from Rivers Inlet and the northern end of Vancouver Island dates back 15 to 20 years and closely matches those data from Line P, a time series in the central northeast Pacific dating back to 1956. All together, there is compelling evidence that heatwaves have occurred on this coast before and may have contributed to ecological shifts in the past.