Is the water in sf bay salt or fresh water?

The water in the San Francisco Bay is saltwater. While it is partially sourced from freshwater creeks and rivers that empty into the bay, and also has some tidal exchange of ocean water at the Golden Gate, its water content has a high concentration of salt, much higher than in freshwater rivers and streams and lower than ocean water. This is what you call brackish water - a blend of saltwater (ocean) and freshwater bodies.