The accident occurred on Sunday, when the two boats collided in the province of Équateur.
One boat was travelling from Ubangi in the northwest to the capital, Kinshasa, and the other from Kinshasa to Lukolela, near the site of the collision.
Fatal boat accidents are common in Congo-Kinshasa, with late-night travel and overcrowded vessels often cited as causes. Lax safety standards have also contributed to hundreds of deaths in boat accidents in the country in recent years.
