Police in Oldenburg said the incident happened shortly before 2 AM today on the Barsseler Tief, a river near the Dutch border.
Police said the dead a 24-year-old woman and a 27-year-old man were sitting in a motorboat that was rammed side-on by another vessel.
Warm weather has resulted in a sharp rise in drownings and watersports injuries in Germany in recent days.
At least four more people died yesterday, including a 10-month-old baby who had fallen into the river Neckar near the southwestern town of Mosbach.
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