We'll give you three things that are related in some way, and it's your job to come up with how they are related. Ready?

The three things are: poisoned fish, industrial pollution, and a contaminated lake. How do these puzzle pieces fit together? The answer most of us came up with probably goes something like this: Industrial pollution contaminates a lake, and the fish get poisoned. However, a study by Swedish researchers has shown that sometimes the story can be more complicated.

The researchers were studying an isolated arctic lake in Alaska, thousands of miles from industrial and other sources of pollution. In spite of its isolation, this lake was still contaminated with PCBs and other pollutants. The fish population was also contaminated. If we stick with our conventional story (pollution gets into lake, then into fish) we would have to find some mechanism for the pollution to get to the lake in the first place, air currents perhaps. The Swedish team has come up with a new culprit: the fish.

The lake in question is visited by spawning salmon, which swim up 250 miles of waterways to get to the lake where they spawn and die. The salmon unwittingly pick up contaminants in more industrial regions of the world, then carry these contaminants in their bodies to the isolated lake. When they die, the pollutants stay in the lake's water, and enter the lake's food chain. It's a fishy solution to a riddle of pollution.