The Matt Lisac Thing.

Tides in oceans and seas happen because of the moon.  When there is a full moon, the oceans come up, because the moon is at its biggest.  Then they slowly recede as the moon gets smaller.  (Gravity is relative to mass.)  The most dangerous time is during a lunar eclipse, which is when the earth sits on top of the moon, and the oceans go all crazy, causing tsunamis and tidal waves.  Tides make blue whales sea-sick, because blue whales are very sensitive to ups and downs.