Ocean scientists experience a certain kind of dread that develops gradually. It doesn’t make an announcement. Data points, satellite readings, and the silent glances exchanged during conferences when another temperature anomaly defies explanation are just a few examples of how it builds up. Since last summer, that dread has been steadily growing off the U.S. West Coast, and it’s difficult to ignore at the moment.
Since 2025, a massive marine heatwave has engulfed Pacific waters, extending thousands of miles from the California coastline and encompassing a large triangle that includes Hawaii, British Columbia, and Mexico. This is only the third time in history that a large portion of the coastal ocean has remained this warm for this long, according to NOAA scientists monitoring the event. More importantly, El Niño, the usual culprit, isn’t to blame. Researchers are alarmed by that detail alone.
The figures are shocking. The northeast Pacific reached its highest average temperature ever recorded on September 9, 2025, at 20.6 degrees Celsius, which was almost half a degree warmer than any previous peak. The West Coast’s waters are about three to four degrees Fahrenheit warmer than usual. The current heatwave briefly resembled the infamous 2013–2016 event that scientists dubbed “The Blob,” which drastically altered Pacific ecosystems to the point where its effects are still being researched. The Blob resulted in years of disturbed fisheries, cascading food chain failures, and species extinctions. Seeing something similar emerge again was grimly familiar.
This one’s behavior makes it more difficult to read. As fall approaches, marine heatwaves typically become weaker and move away from the coast. In October and November of 2025, this one accomplished just that. It then reappeared and grew stronger in the months that followed. The conditions are difficult to reconcile, according to research oceanographer Andrew Leising of NOAA’s Southwest Fisheries Science Center. “We’re in La Niña, but water temperatures along our coast look much different,” he stated. Ocean scientists are kept up at night by such inconsistencies.
Already, marine life is reacting. Due to warming seas, tunas made an unprecedented appearance in Alaskan waters last fall. Warmer surface temperatures in 2025 caused harmful algal blooms that killed hundreds of sea lions, dolphins, and seabirds in a single season, devastating Southern California’s coastal wildlife. When ocean productivity declines due to prolonged warmth, salmon survival rates—which are already precarious—tend to drastically decline. The fishing communities that rely on these species are keeping a close eye on things, hoping that this heatwave won’t penetrate the water column as deeply as The Blob did.
Some researchers believe that the worst is still to come. According to new NOAA forecasts published in May 2026, the heatwave is now predicted to worsen rather than lessen. Another level of complexity is introduced by the potential convergence with a developing El Niño, two separate warming forces that could exacerbate one another throughout the Pacific. University of Arizona atmospheric scientist Kim Wood declared on social media that she was “out of superlatives.” It’s worth pondering that statement.
Whether the warm surface waters will mix and dissipate before causing another significant algal bloom this season is still up in the air. In all honesty, the uncertainty itself is part of the story, and scientists continue to be cautious in their forecasts. Regardless of what forecasting models prefer to believe, the ocean, as Leising put it, ultimately shows where conditions are leading—on its own timetable.
It is evident that the Pacific is not recovering between these two significant marine heatwave events as it once did. Researchers are working hard to determine whether that is a pattern or a coincidence. When the response does come, it is unlikely to be comforting.
