How can alternative practices reduce human impact on waterways?

A waterway is a body of water that can be used for transportation purposes. It is used as shipping route across ocean, seas and lakes. The use of water body for transportation has resulted in the contamination of the water body due to oil spill of water transportation vehicles. Also, the waste from agricultural fields, sewage discharge and industry can be potent contaminants for the water body.

Alternative practices such as creation of walls around the water body so that wastes from surface run off does not get mixed with the water, modification of vehicles so that they do not leak fuel or oil inside the water, addition of water pump to circulate the water so as to prevent algal bloom can be useful to reduce the impact of human on waterways.  

if you listed your answers right then i believe your answer is b.