Tides are a great help in navigation. During high tide when the water level rises, large ships can enter or leave the harbor safely. Diamond Harbor in West Bengal and Kandla in Gujurat are examples of such ports. Tides help ships to travel up the mouth of the river. High tide increases the volume of water at the river ports to such an extent that large ships can sail in safely. They use the retreating tide to leave the port. Hooghly (Kolkata), London and New York are some of the important river ports of the world