Asked by: Vicky Bateman, St Albans
Reptiles have less efficient kidneys than mammals and they can’t produce urine with a higher salt concentration than the seawater they drink. To avoid poisoning themselves with salt buildup, sea turtles have a gland in each eye that actively pumps salt ions into their tears. They need to run these glands continuously to maintain the correct balance of salt in their bodies.
We associate crying with egg laying because that’s the only time they come ashore, but they cry in the sea as well. The tears also help flush sand from their eyes.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.