Yes, bays contain freshwater that mixes with saltwater.
As referenced by Texas Aquatic Science, estuaries and bays are distinct coastal environments formed where rivers meet the ocean. This crucial meeting point is where the process of mixing occurs. Freshwater originating from inland rivers flows into these areas and mixes with saltwater from the sea, such as the Gulf of Mexico.
The reference specifically notes that an estuary, which shares characteristics with or is often synonymous with a bay in this context, is defined as "a partly enclosed body of water along the coast where one or more streams or rivers enter and mix freshwater with seawater."
Therefore, while bays are not composed solely of freshwater, they receive significant freshwater inputs from rivers, which then mix with the existing saltwater, creating a unique environment with varying levels of salinity. The presence and mixing of freshwater are fundamental to the formation and characteristics of bays.
