Would you expect the salinity of the ocean to be high or low in a rainy region near the mouth of a river?

I would expect the salinity to be low. The rainy regions will feed a lot of fresh water to the river that drains into the ocean. This water will dilute the salty waters at the mouth of the river. This is one of the reasons why the salinity of brackish water varies over seasons influenced by the amount of fresh water brought in by the inland river.