If the areas where sea water mixed with fresh water, it is called brackish water and the difference with General Yu River, because here it is a box, and a mess of thousands of years. Cause the gas came up under water.
If the sea area with fresh water. It mingling with the brackish water of different rivers and generally do not. This is a cruise and it is an area with deposits of fossil several years. Cause the gas in waters deeper.
If the seawater and freshwater. It mixed together, called brackish and different with general because the river Here is a box and is the accumulation of fossil fuels for several thousand years. Gas effect on the underwater deeper.