Millions of turtles have been killed over the past 20 years by getting trapped in nets and on fishing hooks, according to a new survey.
Turtles need to come to the surface of the water to breathe, and the animals can't do this if they are caught underwater.
Six out of seven types of sea turtle are now thought to be threatened with extinction.
Experts say they want more people to use safer fishing gear.
And fishing isn't the only danger for turtles.
Rubbish like plastic bags in the oceans can hurt the animals if eaten by mistake.