Answer:
D. By blocking fish migration.
Explanation:
The pictured waterfalls are artificial.
The construction of the wall to raise water level for the falls to be created cuts the contact between marine organisms.
The fish on the other end of the fall cannot freely migrate to the other side.
This is because the falls are too dangerous for them and can lead to their death.
This means that the pictured method of power generation is not environmental friendly.
