Eating fish is generally the best way to get omega-3 fatty acids. (By Web MD)

Eating fish is generally the best way to get omega-3 fatty acids.

But keep in mind that some fish contain higher levels of mercury: king mackerel, swordfish, and albacore tuna. 

The benefits of eating fish are thought to outweigh the risks, but it's a good idea to limit intake of these high-mercury fish.

Info source: http://www.webmd.com/vitamins-and-supplements/lifestyle-guide-11/supplement-guide-omega-3-fatty-acids?page=1