The collision occurred near Laneham just upstream of Torksey, the junction with the Fossdyke, on the tidal section of the river.
It was on Wednesday of this week that the two boats were approaching each other near the sunken islands, and both were in the main channel when they collided, with the narrowboat suffering a split weld, water pouring in and sinking.
There were no injuries, and the narrowboat has been recovered. The incident is now being investigated, with the Marine Accident Investigation Branch involved.
The 'official' interpretation from British Waterways is that 'the narrowboat was rolled slightly during the incident and subsequently took on some water, however did not sink'.