Hydroelectricity was one of the very first technological developments made in US energy industry. Since the first hydroelectric plant opened in 1887 in San Bernadino, California, hydroelectricity had become one of the major sources of electricity production in US as shown in figure 1, second only to coal in its early days . However, the contribution to the total US electricity production from hydropower has been decreasing consistently over the last few decades. The US hydropower has never quite reached its potential.
Figure 1: Timeline of various power production plants in US (1949-2012) 
At large scales, hydroelectricity is the most efficient power production technique, reaching efficiency of up to 95% as shown in figure 2 ,. It is a renewable source of energy which, in fact, helps fight climate change since it does not produce harmful gaseous emissions at a rate anywhere close to what other power plants operating on coal, gas, or oil produce. The advantages of hydropower are countless. It is fueled by water and therefore, it is free and abundant. The fact that it does not rely on any other natural resources, and that water cycle around the world is capable of constant and reliable electricity production, makes it extremely reliable. It is available when needed and can be easily controlled. In addition, large dams built for hydropower plants are a huge asset at the times of flood and drought. They also help maintain the quality of water .
Figure 2: Efficiency of various power plants
On the other hand, there are some downsides of hydropower plants, the most problematic of which is the construction of huge dams. Expensive to build dams, not only require operation of such power plants for decades for the payback, but they also cause some alarming environmental concerns. They can cause some serious geological damage. They require accumulation of large water bodies and therefore destroy the habitat around them. Construction of large dams can also alter the natural flow of water, fish migration, and eventually the surrounding ecosystem . Upstream migration of fish can be severely impacted because of this. Hence, it is obvious that most of the concerns relating hydropower are because of the dams.
But, is there a way around this whole issue of building dams? Can we take the most efficient power production system we have and turn it into an even more efficient one? The answer to that maybe a damless hydropower. Researchers have shown that hydropower can be generated without establishment of such dams and therefore negating all the concerns that arise with them.
The only difference between a dam-based and a dam-free hydropower is the presence or the absence of a dam. The same water current turns the turbines which generate electricity. As shown in figure 3, damless hydropower does not need a dam to create pressure and uses natural flow of the river or tide to produce electricity. Such turbines are low head installations that have very minimal environmental impact. The developers of damless hydropower also claim that the blades turn slow enough to allow fish to escape, and therefore do not affect the fish migration the way dams do. Another important advantage of damless hydropower is that the turbines can be site-based and optimized for performing in certain unique situations. Each power plant can be studied on a site by site basis for optimal performance.
Figure 3: A typical damless hydro turbine 
Damless hydroelectric production has been studied for quite a while now and researchers have found that installing electricity generating turbines under water is practical. For example, Hydro Green Energy, LLC has been testing a damless hydroelectric power plant in Hastings, Minnesota. A 2007 Electric Power Research Institute study estimated that there is a potential for adding a 300 megawatts of damless hydropower in the US by 2025. Federal Energy Regulatory Commission (FERC) could play an important role in the establishment of damless hydropower in the future since the same challenges of federal and state approvals that apply to the existing dams, apply to the new technologies as well .One interesting observation is that the US government is so focused at other renewable sources of energy like wind and solar, it may be overlooking the contributing potential of hydroelectricity. More investment into damless hydro is key to its development into a feasible renewable and clean alternative for power production.