What causes the ocean to have two distinct bodies of water that cannot be mixed

Vancouver, Canada is home to some of the world’s most stunning natural wonders, including the Fraser River and Georgia Strait. However, the boundary between freshwater and seawater in these bodies of water may surprise many visitors. Unlike what one might expect, the boundary is not always a distinct line but can be a result of suspended sediments, caused by a scientific process that occurs in the water. Nonetheless, the beauty and allure of these bodies of water continue to draw countless visitors every year. When freshwater from the Fraser River meets the saltwater of the Georgia Strait, the two bodies of water begin to mix together.