Nearly 190 sea turtles were found “frozen to death” along Cape Cod on Friday morning, according to reports. The sea turtles perished en masse because unexpectedly low water temperatures prevented them from safely swimming ashore, NBC reported. The Mass Audubon wildlife sanctuary has said that “once in a lifetime” weather—including high winds and tide—effectively “incapacitated” these turtles. The nature society says it has found more than 400 dead sea turtles this fall. “A lot of the turtles were found frozen in the water still,” said Bob Prescott, Mass Audubon’s director, “I picked up two to three myself that were still in the water, the slushy water.” Scientists believe that shifts in sea turtles’ migration patterns over the last several decades put them at risk. Thirty years ago, these turtles came to Cape Cod in October but now, they tend to arrive in November—when water temperatures are far lower. Because marine waters are warming, turtles are expanding their ranges into potentially dangerous territories, one scientist told NBC. The combination of warming waters and expanded ranges poses a risk to recent successes in sea turtle conservation.