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Rising sea temperatures are turning nearly all green sea turtles on the Great Barrier Reef into females, according to a new study.

The implications of the study from NOAA published in Current Biology are dire: a severe swing in sex ratios could threaten the population’s future. Of the 200,000 turtles in the northern part of the Great Barrier Reef, 86.8 percent of individuals are female. In juvenile turtles, the ratio is even higher, at 99.1 percent.

Sea turtles are a species with temperature-dependent sex determination. As such, the ratio of female hatchlings increases as sea temperature rises. The sex determination mechanism is so delicate that it can tip from male to female with just a change of a few degrees.

“Combining our results with temperature data show that the northern GBR green turtle rookeries have been producing primarily females for more than two decades and that the complete feminisation of this population is possible in the near future,” reads the study, which also received assistance from California State University and Worldwide Fund for Nature Australia.

If you feel like contributing to citizen science, here is a detailed method for determining the sex of green sea turtles.