The boy, identified as Kalpataru Kakoty, drowned last Sunday and his body was recovered from the waters of Kharajan river during the day, official sources said.
Incessant rainfall in catchment areas during the last week has led to a rise in the water level of the Brahmaputra and its tributaries, affecting 15 districts.
Large-scale erosion was reported from Leduamukh area under Lahorighat revenue circle in Morigaon district rendering about 300 families homeless, the sources said.
In Bajali subdivision of Barpeta district, waters of the Kaladiya river breached dykes and embankments at many places, inundating villages and fields.
More than 90,000 people have been affected in the current wave of floods which have submerged over 4,500 hectares of cropland while stretches of roads have also been flooded in several districts.
In Dhemaji district, 12 boats were being used to transport people to safer locations, four in Bongaigaon and one in Barpeta.