Milon managed to swim ashore.
Two friends jumped into Surma River from a bridge at Tukerbazar in Sylhet on Friday, leaving one missing.
The victim is Abdus Samad, 18, son of late Shamsul Haq of Bagbari Naria area in the city.
Quoting witnesses, assistant sub-inspector of Jalalabad Police Station Mohiuddin said that Milon and Samad went to visit the Surma Bridge in the afternoon.
Later, both of them jumped into the river after having a bet.
Milon managed to swim ashore but Samad went missing, he said.
Meanwhile, Additional Deputy Commissioner of Sylhet Metropolitan Police (SMP) Jedan Al Musa said that firefighters rushed in and launched a rescue operation.