There are a few reason that makes hydro-electric energy less used than the fossil fuel energy. The first problem is that the dams require high investment costs, causing it to require a lot of money to get the dam built. Another problem is that the dams infiltrate the wildlife of the fish and aquatic animals around the dam, due to there being a restricted passage out of the river. It is also very dependent on precipitation, so the dams will not be effective in areas that don't get enough rain. Another problem is that the water quality may be affected after going through the dam, causing a more polluted water source. The final problem is that dams require a running source of water and a high area for the water to have gravitational potential energy.