The tidal waves in the sea are primarily due to

Moon is a massive object which is closer to earth as compared to Sun. Hence, it has a large gravitational force associated with it. Just like the Earth exerts a force on the Moon, Moon also exerts a force on the Earth. This force pulls the water on the surface of the Earth towards it. Thereby causing tides. When the Moon is facing a particular part of the Earth, it causes tides in that region.