In what might be one of the world’s strangest Independence Day fireworks displays, Indonesia sank 38 boats seized for illegal fishing this week. Four were local, but 34 of them came from neighboring countries like Vietnam, the Philippines, Thailand and Malaysia.

As part of Indonesia’s 70th Independence Day festivities, five of the boats were laden with small explosives and sent to the bottom of the ocean Tuesday. Indonesia’s Minister of Maritime and Fisheries Susi Pudjiastuti said the mass sinking was a show of strength to make clear that the country is serious about its territorial integrity and maritime sovereignty.

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While the scuttled boats will make cozy new homes for aquatic life on the sea floor, not everyone is pleased. A spokesman for Vietnam’s Ministry of Foreign Affairs told a local newspaper on Friday that he is “deeply concerned” about the sinking of boats belonging to Vietnamese fishermen.

A history of boat-sinking

This isn’t the first time Indonesia has orchestrated a high-profile mass sinking. The spectacle has become a staple of President Joko “Jokowi” Widodo’s administration. On May 20, he ordered 41 boats sunk to commemorate National Awakening Day, including a boat from China. Several more were sunk without a special occasion.

China said it was “gravely concerned" with Indonesia's actions. A Chinese foreign ministry spokesperson was quoted by AFP: "We hope that the Indonesian side can press ahead with fishery cooperation in a constructive manner and safeguard the legitimate rights and interests of Chinese companies."

Taiwan also has many fishing vessels in the area and has been warned against illegal fishing by Jakarta in the past. A Taiwanese diplomat criticized Jokowi‘s methods, saying: “We don’t burn or sink the fishing boats. We just fine and punish and detain, we don’t burn down the fishing boats aggressively like Indonesia.”

Jokowi says his country loses over $20 billion per year as a result of illegal fishing. An estimated 5,000 boats illegally operate in Indonesia’s waters every day.

The festivities

The ships, which have no one aboard and are emptied of oil, are stationed around different parts of the archipelago. When the festivities begin, the event is televised live nationwide.

An official at the maritime affairs ministry says only a few boats are actually blown up with explosives for environmental reasons, while the rest are scuttled in a less flamboyant manner. To avoid harming coral, they are all sunk at a depth of 40 meters or more. Indonesian authorities state that all of the sunken boats underwent due judicial process.

Vietnam has vowed to better educate its fishermen on the appropriate laws and regulations, but it hopes that Jakarta will treat Vietnamese fishing boats with “with a spirit of traditional friendship and strategic partnership.”