Baja California may be part of Mexico but its geographical isolation makes it feel like a destination apart. The Sea of Cortez, which separates the Baja Peninsula from the mainland, draws divers due to an abundance of whale sharks, gray whales, sea lions and hammerheads.
The diving here is in the Sea of Cortez, a unique body of water separated from the Pacific Ocean by the Baja peninsula. It is a young sea, full of nutrients which does mean that the visibility can be lower, but the marine life is plentiful, and that's the draw - you're not here for the coral. Jacques Costeau famously claimed the Sea of Cortez to be 'the aquarium of the world' and by all accounts, it was once absolutely teeming with all manner of amazing marine life. Overfishing in the 80s has had a big impact, but the marine life remains remarkable by any measure.
There are not many places in the world where you can dive with hammerhead sharks, sea lions, and whale sharks all in one day.
Baja is also a world class destination for whale sightings, particularly from November to March. December to March does see a lot of wind and more unpredictable diving conditions, but it's definitely worth it for the chance of whale sightings. Mantas can also be seen by those lucky few, whilst schools of Mobula can sometimes number in their thousands!