The elevated train in Wuppertal is part of a century-old monorail system that is being renovated. First reports say the train hit a platform left by track workers.
The train, on its first run of the day, fell about 30 feet into the river, where it lay on its side. Rescue workers fished victims from water about 2 feet deep.
The elevated train, a technological marvel when it opened in 1901, travels on tracks suspended above the trains on arching girders and is undergoing a major overhaul. Almost all of the 8-mile route runs along the Wupper, which cuts through a narrow valley of old industrial towns about 30 miles east of Cologne.
How many people were on the train wasn't yet known. Many passengers dragged themselves out of the river by holding onto pipes that supply heat to the region. The injured were being cared for at a nearby house until they could be taken to a hospital.
As many as 70,000 people a day ride the elevated train, most of them commuters traveling from three smaller towns to jobs in Wuppertal, population 385,000.
The train has had accidents before, but this was its first fatal crash, said Juergen Eschmann, spokesman of the city public works department.
In March 1997, a technical defect caused the rear car to collide into the front one, injuring 14 passengers. The train also derailed in December 1970, but there were no injuries.