A vast region of unusually warm water has formed in the northeastern Pacific Ocean, and scientists are worried that it could devastate sea life in the area and fuel the formation of harmful algal blooms.

The broad swath of warm water, now known as the Northeast Pacific Marine Heat Wave of 2019, was first detected in early June. Now data from weather satellites and buoys show that it measures six to seven times the size of Alaska, which spans more than 600,000 square miles.

Given its size and location, the marine heat wave rivals a similar one that arose in 2014…