Congolese navy is tasked with preventing militia fighters and local rebels and others from Uganda and Rwanda from operating in the area.
On Saturday, seven Congolese fishermen were killed by the Ugandan navy.
Two days earlier four Ugandan military personnel and three civilians were killed in a skirmish between the two armed forces.
Last Wednesday, a Ugandan patrol boat arrested 18 Congolese fishermen as they were casting their nets.
At least 12 fishermen have died and a dozen more are missing after deadly clashes on Lake Edward, which is shared by Uganda and the Democratic Republic of Congo, a Congolese official said Monday.
"The 12 bodies of our compatriots are still floating on Edward Lake" after violent exchanges between the Ugandan navy and DRC armed forces, said Muhindo Kyakwa, a senior official of the DRC province of North Kivu.
"We can't retrieve them because Ugandan troops are opening fire on anything that moves," he told AFP, adding that "a dozen fishermen" were still missing.
His statement follows an earlier Congolese announcement that 16 fishermen were missing on the lake.
Some 30 people have now either died or disappeared after the clashes erupted late last week.