Drift netting, an outlawed fishing technique, is being used indiscriminately in the northwest part of the Indian Ocean, according to Greenpeace, the international non-governmental environmental organization.

Touted as one of the simplest and oldest methods of fishing, drift nets hang vertically in water bodies to trap fish in the mesh. Commercial fisheries prefer using drift nets since they can trap large quantities of fish, at comparatively minimal costs of installation. Additionally, drift nets do get lost at sea due to storm currents or other accidents. And since they are often made of non-biodegradable materials, they can remain in oceans indefinitely as ‘ghost nets,’ continuing to trap marine animals.

However, since drift nets aren’t selective of the species they trap, they often enmesh non-target species like sharks, turtles, sea mammals, or even seabirds, posing a serious threat to marine ecosystems. On account of their potential to cause mass damage to the environment, the United Nations had banned drift nets longer than 2.5 kilometers in the early 1990s, almost three decades ago.

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But while the ban continues to be in effect, it hasn’t been successful in keeping drift nets out of water bodies. During its two-week-long investigation, Greenpeace found several ships openly casting drift nets to catch fish. The NGO also detected more fishing vessels in the region “using navigational patterns that also suggested use of nets.”

“There is little to no enforcement in international waters. … We need a global ocean treaty … to resolve this enormous governance gap,” Will McCallum, head of oceans at Greenpeace U.K., told Reuters. “What’s the point in a UN ban on driftnets when all the fishing vessels we saw are using driftnets?”

In addition to endangering the ecosystem, drift nets are leading to the decline of marine species at a rate that has begun posing a threat to the food security of locals. It could also impact their livelihoods and jeopardize economies, Greenpeace warned.