Hydropower is the creation of electricity through the damming and then gradual release of water that runs through turbines. The classification of large or megadam scale simply relates to the size of the project; generally, a large scale facility has an energy capacity of over 30 megawatts. Above that, we consider it a megadam. In North America, the Upper Churchill facility in Labrador, Canada on the Mista Shipu (or Grand or Churchill River) has the highest capacity in North America at 5,428 megawatts and can expand to 9,252 MW with the proposed Lower Churchill project at Muskrat Falls.
Hydropower from the Upper Churchill megadam is used in Massachusetts and other New England states. (Hydro-Quebec has a long term contract with Nalcor Energy to buy the hydropower from the Upper Churchill dam.