What raises and lowers the boat to the level of the water?

It is the locks in the canal. They raise and lower the water

2 pairs of lock Gates are sited in a canal and act to separate the high water level from the low water level. These are large gates which are hinged such that they can be fully open or fully closed. They can only open when the water level is the same on both sides of one particular pair .This action is typically carried out manually

Sluice gates are small gates which are built into all four lock gates . Water acting under the force of gravity will fill the space between each pair of lock gates. By selectively operating the sluices the water level between the 2 pair of gates can be exactly the same as the high water level or exactly the same as the low water level.

The purpose of the system is to allow barges to be raised from low to high or conversely lowered from high to low. Obviously the barge has to be positioned between the pairs of gates when the water movement occurs.