Drakes Estero is a pristine bay off of Drake Bay on the Pacific Ocean. Due to its location, about the only water use you will see are other kayakers and maybe the oyster company's motorboat. It is protected from the ocean through a sand spit at the far end.
You will likely see lots of wildlife on a paddle here. Harbor seals are all over the place. If you paddle out towards the mouth and then left into Estero de Limantour, you may get to see leopard sharks and rays.
The Estero is tidal, and the currents (particularly out near the mouth) can get rather strong (2-3 knots). And much of the Estero is shallow, so becomes mud flats in low tide. The zone where the tidal currents meet the waves at the mouth can be very choppy, with standing waves.
The Estero is closed from March to June(probably some animal's breeding season - sorry I don't have details).
Pit toilets at the launch point.
Blue Waters Sea Kayaking is the local outfitter (in Inverness). They lead guided trips there and have information on the Estero, but have stopped renting take away boats for the Estero due to some agreement with the Oyster Company (they will rent for a paddle on Tomales Bay - see other destination reports).
Get to Highway 1 and Sir Francis Drake in Olema, CA by the best route available. Take Sir Francis Drake West from there. Go past Inverness a few miles until you see the water on your left, and the dirt road called Oyster Company Road. Take this road to the end.
National Park Service - http://www.nps.gov/pore/
Details and a map of Drakes Estero at http://en.wikipedia.org/wiki/Drakes_Estero.