The Atlantic and Pacific oceans meet at the southernmost tip of South America. So why are the water levels different on each side of Panama, necessitating the use of locks?

In fact, water levels on the opposite sides of Panama average less than a foot different, mostly due to currents, tidal variations, etc. The canal needs locks in order to raise ships high enough to cross the Continental Divide. The ships traverse man-made Gatun Lake about 80 feet above sea level and are then lowered to head downward on the other side. In other words, even if sea levels were exactly the same on the Atlantic and Pacific sides, the Panama Canal would still need locks.