Tides in theory
I am pretty sure that all of you PADI Divemaster and future IDC candidates where once standing on a beach and the sea looked like that picture here in Sanur, Bali. My nephew even asked me once a couple of years ago; “uncle I don’t know but somebody stole the water, seriously!! :)” After a laugh I simply explained to him that this is because the sun and the moon are facing each other and battling for the water.