Farmed salmon are raised in open cages, thousands of them in a net-pen the size of a small house. Usually, a dozen or so of these pens are tethered together. The fish pass their feces right into the waters around them, contaminating the water with as much raw sewage as a town of 65,000.

Diseases and infestations can spread rapidly in crowded pens where salmon are raised. Fish farmers dose their fish to combat these outbreaks, using seven tons of antibiotics in British Columbia in 1998 alone.

Still, epidemics can infect and decimate wild stocks. The 2002 collapse of the pink salmon run on the central B.C. coast is blamed on parasites known as sea lice, contracted from the area’s numerous salmon farms.

If you haven’t seen the word “wild” at the market or on the menu, the salmon you’re eating is probably farmed. Farmed salmon are raised in floating feedlots in Chile, Canada, Europe, and the United States. And that spells trouble. For you, for wild salmon, and for the oceans.

How can a food be so inexpensive in the supermarket but so costly both to our well-being and the environment? It’s because the economic groundrules hide the real costs.

In the case of farmed salmon, those rules allow raw sewage to pour into coastal waters, and fatal epidemics to spread from farmed to wild fish. Meanwhile, the industry dodges the bill, leaving you, me, and our children to pick up the tab. Many people think that buying farmed salmon saves wild fish. Think again.

Wild salmon get their beautiful hue from the prey they eat. But their farmed cousins rely on a dye to color their flesh pink. Without that added pigment, their meat would be a pale gray.

Salmon farms don’t protect wild salmon. Instead, they infect wild fish with parasites and diseases, and compete for precious habitat when farmed fish escape their pens.

If you frequently eat fish and seafood, you need to be aware of where that food is coming from.

China—the leading exporter of seafood to the United States—has been found to raise most of its fish in sewage-infested waters. To compensate for the lack of clean water they pump in antibiotics, fungicides and pesticides—many of which are banned carcinogens here in the United States.

In the last year, the United States increased its imports of seafood from China by 34 percent. Meanwhile, one in four Americans gets hit with a food-borne illness each year. About 20 percent of these cases are due to contaminated seafood.