Minecraft wiki entry for Turtle_farming, associated text: You can modify the barrier by installing a gate made from trapdoors under the barrier. The trapdoors can be operated manually, or you can lay a line of redstone dust on top of the barrier with a lever somewhere to power all the trapdoors at once. This can be used to keep adult turtles from leaving until you have fed them and got them to mate. A pregnant turtle needs to return to the water before returning to the beach to lay eggs. She may do this by returning to the water in the farm, and you might need to attract her back out onto the beach with seagrass. Otherwise, let them leave the farm and you can induce them to re-enter it later. A pregnant turtle fits under the trapdoors when open.