All it takes is a few seconds—and a big boom—to destroy an underwater ecosystem decades or centuries in the making.

The boom, in many cases, comes from a homemade bomb thrown overboard by someone looking for a quick and easy way to collect fish. The blasts kill or stun the fish, which can then be scooped out of the water with little effort.

“It costs $1 or $2 to create this bomb,” said Gabby Ahmadia, a senior marine scientist with the World Wildlife Fund. “They might be able to get $10 or $15 worth of catch.”

That relatively small amount of catch, however, comes with a huge cost below the surface of the ocean. Ahmadia just returned from three weeks in the Pacific Ocean’s Coral Triangle, where she observed the effects of blast fishing. “I’ve seen reefs that I’ve been working on for years, and they’ve been blasted,” she said. “They look like huge rubble minefields. It’s sad, because you have this beautiful 3-D architecture that a healthy coral reef can provide, and when it gets blasted all it ends up being is this rubble field that doesn’t have that nice habitat for all of the fish and other critters to live in.”

Coral reefs take up about 1 percent of the ocean bottom, but they are home to more than 25 percent of marine fishes.

(See Pete Bethune and his team investigate blast fishing in this week’s episode of The Operatives, which airs on Sunday, Dec. 6, at 8 p.m. ET/ 5 p.m. PT on Pivot, the television network owned by Participant Media, TakePart’s parent company. Join the Operatives on their missions, and take action to protect all wildlife by clicking here.)

The effects of this blast fishing are long-lasting. “After the 30 seconds that it takes for the blast to go off and damage the reef, it can take decades for the reef to recover,” Ahmadia said. Meanwhile, the myriad marine life that used to live in and around the reef disappears. “Imagine going to a rainforest and there’s all these creatures sitting there, and then you move around to an area where it’s been clear-cut and it’s empty of wildlife. Essentially that’s the same thing you’re seeing underwater.”

RELATED: One of the World’s Most Notorious Illegal Fishing Crews Is Fined $17 Million

Ahmadia said the blast fishing technique is particularly prevalent in Indonesia and that the people who use it know the damage they are creating. “They won’t blast along their own reefs,” she said. “Often they’ll go out to other reefs or to remote places, because they do understand the repercussions.”

The practice continues even though it’s dangerous for the fishers as well. “You often see people with missing limbs or a lot of burns all over their bodies,” Ahmadia said. “People are like, ‘Yeah, that’s a bomb fisher.’ ”

Although bombs are the most prevalent, they aren’t the only illegal fishing technique that can harm coral. Large nets or traps can break coral, causing irreparable damage. Some people also use poisons such as cyanide. The poison stuns the fish, making them easy to catch, but after that it kills coral and other sea creatures. According to the WWF, for every fish that is caught using cyanide, about a square meter of coral reef dies.

More large-scale use of these methods can also cause damage to the lesser-known deep-sea reefs that grow many hundreds of feet below the surface. Sometimes these actions are deliberate; other times they are done out of ignorance. “For the most part, fishermen are not targeting these habitats, but in many cases we don’t know where these habitats are, so it’s easy to blunder into areas and damage them,” said Tom Hourigan, chief scientist for the deep-sea coral research and technology program at the National Oceanic and Atmospheric Administration.

Even unintentional damage adds up—and it doesn’t go away. “Heavy fishing equipment, especially heavy bottom trawls, can do a lot of damage to these habitats,” Hourigan said. “Some of the habitats that have been damaged by trawling or other fishing techniques, there’s very little evidence of recovery after several decades.”

NOAA, the WWF, and other organizations and governments have helped to combat illegal fishing by establishing marine protected areas and funding enforcement and prosecution of illegal fishing. They also work to educate communities about the destructive nature of these practices.

The MPAs don’t cover everything, though. Ahmadia recounted a research effort from a few years ago when she was trying to find previously healthy reefs just outside an MPA. During a three-day search, all the team could find “was rubble field after rubble field after rubble field. Because this was a more remote area, they had just decimated it. That’s pretty depressing,” she said.