Lunar/Solar Tides (exaggerated!)
From the text, Horizons by Seeds
What are tides?  More complex than what you see on Baywatch!
Gravity from the moon and sun pull on Earth.  Gravity weakens with distance, so the pull is strongest on the near side, weakest on the far side.
The sun is more massive than the moon, but farther away, so its tidal effect is smaller.
Actual flow of water around the world is very complex and not fully understood!