Marine heat wave raises ocean temperatures off California coast

A marine heat wave has developed across much of the West Coast, stretching from Washington to California. In some areas, ocean temperatures have climbed 4 to 8 degrees above average. At the Scripps Pier in San Diego, ocean temperatures have logged record-high readings on more than 30 days through April.

The warmer water is disrupting the food chain. Seabirds are washing up on beaches weak, starving, and in some cases dead as fish move farther offshore. Wildlife rescue centers report more underweight and exhausted birds arriving for care. At the International Bird Rescue Center in Fairfield, staff are caring for about 20 pelicans suffering from starvation.

Nearly 50 more are receiving treatment at the organization's Southern California hospital in San Pedro. A similar marine heat wave in Australia two years ago was linked to more than 600,000 seabird deaths, according to a study published in Conservation Biology.

Researchers noted that most carcasses never reach shore, making full mortality counts difficult. During the 2014-2016 marine heat wave known as "The Blob," an estimated 62,000 Common Murre carcasses washed up on beaches from California to Alaska. Researchers believe the true number may have reached one million birds.

Young sea lions were also affected as prey moved deeper or disappeared.

Persistence of the heat wave The marine heat wave, identified as NEP25A, reached a record size for the region in September 2025, covering about 10 million square kilometers of the Northeast Pacific. It contracted before re-intensifying in December and has remained unusually warm through winter and into spring.

Coastal sea surface temperatures are among the highest ever recorded for this time of year. NOAA's April analyses show large portions of the U.S. West Coast, particularly off California, remain affected. The event has at times rivaled the 2014-2016 heat wave in spatial extent but has not matched it in duration or depth of warming.

Forecast models indicate conditions are likely to persist through spring and summer, with an increasing chance of coastal warming as the region may transition toward El Niño later in 2026. As of April, NOAA classifies the climate system as ENSO-neutral with an El Niño watch in place for later in the year.

Additional effects Harmful algal blooms can form in the warm, slow-moving water, sometimes producing toxins that lead to beach advisories or temporary closures. Shifting conditions have also resulted in more frequent reports of jellyfish and other stinging organisms in some areas.

Fish species often move deeper or farther offshore in search of cooler water. Shellfish harvesting can be disrupted during toxic bloom events, prompting temporary fishing restrictions. These changes can affect seafood availability and pricing across California.

A marine heat wave is defined by the National Oceanic and Atmospheric Administration as a period of unusually warm ocean temperatures lasting days, weeks or months. These events are driven by shifts in ocean currents, persistent weather patterns and larger climate systems such as El Niño.

Oceans have absorbed about 90 percent of the Earth's excess heat energy over the past 50 years. In March, ocean waters along parts of the West Coast were about 3 to 4 degrees above normal. Each of the past nine years has set a new record for ocean heat content.