Mafia Island Marine Park, Marine reserve in Mafia Island, Tanzania

Mafia Island Marine Park is a 822-square-kilometre protected area of IUCN category VI around the Mafia Archipelago in the Indian Ocean, administratively in Mafia District of Tanzania's Pwani Region. It lies southeast of Zanzibar Island and takes in coral reefs, mangrove forests, river estuaries and marine channels.

The park was established in 1995 after decades of damage from dynamite fishing and illegal coral mining had depleted the marine ecosystem. This action marked a turning point in efforts to restore the region's ocean life.

Local fishermen reported a steady decline in catches from the 1960s, blamed on dynamite fishing, habitat destruction, overfishing and destructive gear, with the lowest catch per unit effort in the 1980s and 1990s. Studies after the park's creation found that villagers lost key fishing grounds and that management prioritised marine conditions over human needs. Coral mining is now allowed only for subsistence use.

The park lies in Mafia District, Pwani Region, around the Mafia Archipelago in the Indian Ocean. Boats reach the reefs and channels from the island's villages; snorkelling and diving are the main ways to see the marine life. Coral mining inside the park is now allowed only for subsistence use, so do not take coral or shells.

Mafia Island is known for an offshore resident population of whale sharks, the largest fish in the sea, which can be seen near the park's waters. The park also covers a stretch of the Indian Ocean's sea of Zanj around the Mafia Archipelago, southeast of Zanzibar Island.