Tides originate in the oceans and progress toward the coastlines where they appear as the regular rise and fall of the sea surface. When the highest part, or crest, of the wave reaches a particular location, high tide occurs; low tide corresponds to the lowest part of the wave, or its trough.

Are tides only in the ocean?

Indeed, tides exist in all bodies of water, even one's bathtub, but is so infinitesmally small, as to be unmeasurable. Even on Lake Superior, the largest of the Great Lakes of North America, the tiny effect of a tide is overcome by the effect of barometric pressure and the phenomenon known as a seiche.

Do tides occur everywhere?

In most places, but not everywhere, there are two high tides and two low tides a day. The difference in height between high and low tides varies, as the moon waxes and wanes from new to full and back to new again. The moon and sun are primarily responsible for the rising and falling of ocean tides.