While this year’s El Niño wasn’t as bad as meteorologists were expecting, there’s something else wreaking havoc on North America’s marine ecosystems: a huge mass of warm water off the Pacific Coast nicknamed by University of Washington meteorologist Nick Bond “the blob.”

It’s not a creature from a horror flick, but it might as well be for marine scientists. The blob was first noticed on the surface of the Pacific in 2013 (pdf), and some weather experts declared it dead last December. But the blob isn’t dead—it’s just retreated to deeper parts of the ocean, according to recent findings.

The Canadian Coast Guard regularly measures the ocean’s temperature at different depths off the coast of British Columbia, and found that rather than sitting at the surface of the water, the blob is now hovering between 150 and 200 meters (about 500 to 650 feet) below. “The residual effect of the blob is still there,” Canadian scientist Ian Perry told CBC News this week.

The blob’s effects have been anything but benign, according to a new study, published Wednesday in the journal Geophysical Research Letters by a team of researchers from the University of California, Santa Cruz, Scripps Institution of Oceanography and the National Oceanic and Atmospheric Administration. The study presents evidence that the blob was responsible for more ecosystem damage off the California coast, including depleted marine food sources and disrupted migration patterns, than the 2015-2016 El Niño weather system.

Scientists aren’t quite sure how the blob developed. It isn’t a result of El Niño, or another ocean cycle called the Pacific Decadal Oscillation, which is a pattern of oceanic warming and cooling that occurs on a much larger timescale than other weather patters.

What they do know is that its timing with El Niño wasn’t great. While El Niño was weaker along the California coast than meteorologists predicted, it worked in tandem with the blob. “In their wake lies a heavily disrupted ecosystem,” study author Michael Jacox said in a press release.

The plankton population in Californian waters took less of a hit than during El Niños past, but the researchers suggest the blob may lead to lower plankton numbers for a longer period of time. These microscopic organisms that float in the ocean water are critical for the health of marine ecosystems. They photosynthesize and add oxygen to the water, and they’re an important food source for many fish and whales.

Fewer plankton isn’t the only sign of trouble. Crabs that normally live in the open ocean washed up on California beaches last year, and sightings of humpback whales have been reported much closer to shore than usual.

As for the future of the blob, it seems an upcoming La Niña might deliver the fatal blow, bringing the warm water back down to a reasonable temperature. Nick Bond told CBC News this week that because the blob is so warm, cooling down is “going to take a while—at least through the remainder of this year.”