In the first incident in Jamui district, at least five persons drowned when a country boat capsized in deep waters at Garhi dam, Officer In-Charge of Garhi police station Ram Narain Rai said.
Seven others are still missing and search is on to find them, he said.
Rai said 16 persons were on board the boat in which four swam to safety.
They were going to Garhi village for a religious function from Kauwakol village in neighbouring Nawada district, the OC said.
In an another incident in Begusarai district, one person drowned in Balan river while six others swam to safety, District Magistrate Seema Tripathi said.
Seven persons on board were returning to Mansoorchak village after watching a cultural programme in Bharaul village when the mishap took place, the DM said.