The St. Lawrence Waterway has many locks. What do locks do? Why are they needed on some canals but not others?

Question

The St. Lawrence Waterway has many locks. What do locks do? Why are they needed on some canals but not others?

Answer 1

locks will move a ship up or down to different water levels, and are usually powered by gravity. ive been through panama atleast 4 times, way cool. they raise a ship to the lake level, you sail through and then you go back down.

  the ship takes on a pilot to navigate the waters, its freshwater and the ship pays by the ton.