While Hawaii residents and visitors have been sweating out a lack of trade winds, corals underwater are also suffering.

Scientists standing in the muggy heat at Heeia Small Boat Harbor in Kaneohe said Monday that they’re seeing more evidence that higher-than-normal ocean temperatures are killing algae, which starves coral and turns it white.

Mass bleaching had already been seen about 1,000 miles northwest of Honolulu, and now Hawaii’s Department of Land and Natural Resources says crews have found especially severe bleaching along Oahu’s windward coast.

Scientists note this September was the second-hottest on record since the 1940s, with recent underwater temperatures as high as 86 degrees. A maximum of 83 degrees is normal.

Scientists say the warm temperature is adding to the stress factors coral already face, such as pollution and being trampled upon.