Question

what is the main reason why many nuclear power plants are located near bodies of water?
to wash wastes out of the power plant
to be close to shipping lanes for frequent fuel delivery
to have easy access to a coolant for the reactor
to avoid problems with water supply during a drought

Explanation:

Nuclear power plants generate a large amount of heat. Water is an effective coolant. Having easy access to a coolant (water from the body of water) is crucial for cooling the reactor. Washing wastes out is not the main reason. Shipping lanes for fuel delivery is not the key factor as nuclear fuel is not frequently delivered like some other fuels. Avoiding water - supply problems during drought is a secondary consideration compared to the need for a coolant.

Answer:

to have easy access to a coolant for the reactor