Now, the capital is turning to new technology to help pinpoint the litter so that human divers can scour it off the seabed. This past Thursday, board members of Oslo’s Port Authority approved a pioneering trash-removal plan.

“We will test out drones,” said Svein Olav Lunde, the chief technical officer of the Oslo Port Authority, shortly after the meeting, explaining how these unmanned vessels will be used to help clear out underwater “islands of trash.”

Geir Rognlien Elgvin, a board member, says he believes that Oslo’s port will be the first in the world to try this sort of trash pickup. The drones will plunge into the depths of Oslo Fjord this spring. An electric-powered ship with a crane will join the cleanup fleet by next year.

Oslo is turning to drone technology partly because of a dead dolphin — bloodied, beached and ensnared in plastic. Gory images of the carcass, taken in January on a trash-strewn shore of Oslo Fjord, resonated on social media among Norwegians, who tend to see their jagged coastline as a paragon of untouched natural beauty.

Mr. Stubberud said that recent images of beached dolphins and whales have woken up Norway, but that “plastic is the real problem.” Politicians and the public have shown more interest in the cleanup campaign in the past two years, he said.