I remember hearing that you shouldn't go swimming in the ocean when you had your period or you would attract sharks.
A childhood belief about periods

others believed things like this
- I used to believe that the waves in the ocean were made from whales swimming by...— Tina
- I used to believe that if you went swimming after you got your first period, then you could get pregnant. — Mel
- I remember being scared of the ocean for a while as a little kid. I thought lobsters would pinch my toes.— Flipper
- I used to believe (about 9) that a penis was a sausage that men stuck in their crutch area to attract women.— Feebs.
- I used to think that the song "My Bonnie Lies Over the Ocean" was really "My Body Lies Over the Ocean."Anon
- I used to think that when you swimming 'Freestyle' was swimming any way you want.Anon