The last salmon filet you had probably never swam freely in the sea. Chances are it was born and raised in a net pen on a fish farm in Northern Europe, Chile, or Canada. Aquaculture—raising marine species in environments controlled by humans—brings in a lot of cash, especially for popular delicacies like salmon. And since the United Nation’s Food and Agriculture Organization predicts that by the year 2040, there will be no more fish in the oceans, aquaculture may be the wave of the future.

But environmentalists argue that aquaculture is a major source of pollution. Farmed salmon are raised in small net pens in the ocean. To control diseases and parasites, producers use antibiotics and chemicals which pollute ocean waters. The salmon farming industry is working hard to develop environmentally friendly technologies such as closed-containment systems that would separate the ocean’s ecosystem from the polluted waters of salmon farms.

Still, supermarket buyers worry about the fishing industry meeting high demand for the popular fish. Recently, salmon fishing was banned for one fishing season in some areas in western parts of the United States due to depleting fish stocks.