Output at Peligre has been down since Monday, EDH said, after people stormed the plant demanding other areas be supplied before the capital, Port-au-Prince, where some residents are relying on diesel-powered generators and solar batteries.
The capital's poorest residents cannot afford either alternative.
"Such actions, far from helping meet the population's electricity needs, make EDH's challenges even more difficult as the equipment used to operate plants are expensive and hard to repair, maintain or replace," EDH said in a statement.
It called on authorities to urgently take necessary measures to secure the plant, a structure of "strategic importance to the Haitian state."
With a capacity of 54 megawatts (MW), Peligre provides nearly all of EDH's 60 MW of hydroelectric power, Haiti's largest source of electricity after fossil fuels.
Just 49% of people in the Caribbean nation have access to the electricity grid, according to the latest World Bank data.
EDH said two transformers had been irreversibly broken, and it was unable to bring in technical assistance because the Ouest department, where Port-au-Prince is located, has been virtually cut off from the rest of the country.
Haiti is battling a humanitarian crisis that has seen violent and powerful armed gangs take over much of the capital and surrounding areas, cutting off safe transport as well of key supplies of goods such as medicine and food.
Nearly 580,000 people have been internally displaced and close to 5 million are facing severe hunger.
E-Power, a private firm that operates a 30 MW heavy fuel oil power plant in Cite Soleil, one of the capital's hardest-hit neighborhoods, is another key energy supplier in Haiti.
Prime Minister Garry Conille visited the plant alongside the head of EDH last month, which his office said was in order to evaluate the facility and consider how best to improve Haiti's electricity challenges.
