The salinity of the of the water located near a rainy region of the mouth of a river would be expected to be lower than the rest of the ocean.

 Salinity is a measurement of all the salts in a solution. Salinity is usually measured in parts per thousands, which can be abbreviated as ppt. On average, the salinity of an ocean is about 35 parts per thousand. This means that there is about 35 grams of salt in every 1,000 grams (or 1 kilogram) of ocean water. The average salinity of a river is, on average, about 0.5 parts per thousand. This means that there is about 0.5 grams of salt in every 1,000 grams (or 1 kilogram) of river water. However, if it had recently rained near the mouth of the river, then the salt concentration would have been diluted to an even lower value.