The mysterious malady was first identified in August, and reports have steadily been increasing ever since.

"This summer is the worst recreational fishers, and our Kai Ika Project filleters have ever seen," Trish Rea, a fisher and analyst for the non-profit marine restoration group LegaSea, told Newsweek. "On some fishing charter boats there are more fish with milky flesh than without."

The milky fish have been spotted throughout the Hauraki Gulf Marine Park, which spans 1.2 million hectares off the coast of New Zealand's North Island.