The bridge to Puerto Corinto in western Nicaragua suffered cracks in the Saturday evening attack, which came amid anti-government protests. The bridge has since been repaired, according to Reuters witnesses.
"My son was captured on Sunday at four in the afternoon," Nubia Sandoval, the mother of one of the three suspects arrested, Douglas Villanueva, told Reuters.
Sandoval said her son had taken part in protests against the government, but denied he had anything to do with the attack.
The others arrested were Carlos Cardenas and Henry Lara, opposition activist lawyers from a political party in the nearby city of Chinandega, said Roberto Lira, a friend of Cardenas.
Cardenas was arrested on Monday, Lira said. He said neither Cardenas nor Lara were involved in the bridge attack.
Police have not provided information about the blasts or the detainees, and did not reply to a request from Reuters for comment.
The government also did not reply to a request for comment.
Nicaragua has been in the grip of a political crisis since demonstrations broke out against the government of President Daniel Ortega in April 2018 over planned welfare cuts.
The demonstrations spread into broader protests against Ortega, and clashes between pro-government forces and protesters have claimed more than 300 lives and prompted thousands of Nicaraguans to go into exile, human rights groups say.
A little-known group opposed to Ortega, the Nicaraguan Patriotic Alliance, claimed responsibility for the weekend attacks, which included not only the bridge bombing but also homemade bomb blasts in Managua and the city Masaya.No significant damage was reported in the Managua and Masaya attacks.