The Bristol Channel, which separates Southern Wales from the Southwest of England, has some of the highest tides in the world. At one point, the government was intent on building a huge tidal barrage which, it was claimed, might provide between 5 percent and 10 percent of the U.K.'s energy needs. But the plan proved controversial among environmentalists, with many arguing that the disruption to ecosystems was too high. Instead, focus has now shifted to tidal lagoons which will be much less disruptive, while still providing power to hundreds of thousands of homes. The proposed lagoon in Swansea Bay, shown in the video above, is just the first of several planned installations around Britain, three of which should be operational by 2021.