Yep that's right... as are the other nations of the planet. Most people believe that when they trek to the beach they are pretty much at the end of the country or can at least see its borders on the horizon. In actuality the sea waters extend quite far out. But that's not what I'm talking about.
While every nation is allowed a certain amount of the sea as part of their territory extending up to 12 nautical miles and up to 200 for economic purposes, the extent of a country can go much farther than this.
What am I talking about? I'm talking about what was dubbed by President Truman as the 'Natural Prolongation' of land. Under this a country's territory can extend well over the 200 nautical miles where the landmass (or the mountain) extends under the surface of the sea. This only includes the land part found under the sea. Anything in the water above it doesn't belong to anyone.
Sadly for us, though we have a large extension of land Sri Lanka has been 'slow' to register the land prolongation and it will be a few years till the claim goes through. In that time any other country could harvest any resources located outside out the 200 miles, especially since we don't have the technology to harvest it ourselves. No one is saying that there are resources, but if there were...
I'm sure its a little more complicated than this, but it is the basic idea. This can be seen in the image.