No group has claimed responsibility for the attack, which took place on Wednesday, but the region around Ituri province has been by violence between militias from the Hema and Lendu communities.
"Nineteen corpses were found in the village of Tara on the edge of Lake Albert, and eight others were wounded," said Pilo Mulindo, a community leader in Djugu territory.
"Armed bandits attacked a group gathered on the beach to set up a market," the official said.
The UN mission to the DRC, MONUSCO, reported the attack without giving a precise death toll. It said it planned to send a team to the area.