A boat carrying some policemen to the southern Ijaw Local Government Area of Bayelsa State, capsized on Saturday.
Channels Television reported that they were traveling to the area to monitor the senatorial bye-election.
Although the police has yet to confirm the number of victims, at least three policemen are said to have drowned.
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Bye-elections were held in 11 states across the country, covering six senatorial districts and nine state constituencies.
Lagos and Cross River States held elections to fill vacant senatorial and state assembly seats while the other nine states either held senatorial or assembly elections.
The bye-election originally scheduled for October 31 was postponed by the Independent National Electoral Commission (INEC) following the #EndSARS protests and the violence that resulted when thugs took over the protests.