Differences between ocean water and river …

Salinity

Perhaps the biggest difference is in the name itself. Saltwater contains salt, or sodium chloride. Freshwater may contain small amounts of salt, but not enough to be considered saltwater. Ocean water has an average salinity of 3.5 percent. 

Density

Saltwater is denser than freshwater due to the sodium chloride dissolved in it. This means that a specific volume of salt water is heaver than the same volume of freshwater. Warmer salt water is less dense than colder saltwater, which results in the colder water sinking to the ocean floor. While colder water is denser, when water freezes into ice, it becomes less dense and floats on the surface.

Freezing Point

Both the freezing and boiling points of ocean water differ from freshwater, but only the freezing point is of concern in nature. The average freezing point for ocean water is -2 degrees Celsius, although it can be even lower than that if the salt content is higher or the water is under pressure. The typical freezing point for freshwater is 0 degrees Celsius.