[cjensen]

That's close to literally impossible.

There was an absurd plan to place a dam between Richmond and San Rafael[1]. When it was finally studied, there were two fatal problems with the plan. (1) There is not enough water in Summer, to keep the bay behind the dam full. (2) There is too much water from snowmelt in early spring and the San Joaquin valley would turn into a lake.

Now to the environmental side: the bay is amazingly productive. It also acts as a nursery for the ocean. The damage done to the Pacific Ocean ecosystem would be all out of proportion to the gains of a little bit of land.

[1] https://en.wikipedia.org/wiki/Reber_Plan