Late-Summer and through late November provide some of the most phenomenal diving to be found worldwide, right here in the Sea of Cortez. Enjoy a first-hand story of playing with sea lions, chasing dolphins and seeing some of the finest underwater scenery in the world.

After hearing mixed reports about the diving in Baja California, I had consciously pitched my expectations at a low level, but as the Aero California jet crossed the narrow isthmus of northern Baja at dusk and the glistening expanse of the Sea of Cortez came into view, excitement came bubbling through and I could hardly wait for the diving to begin.

Next morning Hilary, our daughter Rachel and I were speeding out of the bay of La Paz in one of the dive boats, on our way to Los Islotes, a series of small, eroded rocky islets to the north of Isla Espiritu Santo. As we headed out to sea the deep blue water contrasted with the ochres, grays, and browns of the stark but spectacular mountains of this desert peninsula. Frigate birds hung overhead, their long, pointed wings and long, powerful beaks recalling the pterodactyls that once soared over this ancient landscape. 

Dozing California Sealions were scattered about on the rock ledges at Los Islotes when we arrived and some of the old bulls barked loudly at us as we kitted up and went in over the side. Ah, what a wonderful feeling it is as one passes through that mysterious barrier between air and water, the bubbles clear and one is once more in that strange another world down below! A very different landscape from the usual coral reef scenery was to be found here, with piles of boulders, virtually free of coral, tumbling down to a sandy flat.

Fish were numerous and most were endemic species of the Eastern Pacific. There were droves of little Scissortail Damselfish, strange hump-headed Mexican Hogfish, huge Cortez Angelfish, Barberfish, a vortex of Mexican Barracudas and huge schools of wriggling Green Jacks and Flatiron Herrings. Best of all was a Pacific Seahorse we found attached to a gorgonian, so big that it dwarfed all those I had seen in the past.

But where were the sea lions? First, a few large females swept past, ignoring us, but then as we approached the reef wall a large pup came shooting down from the surface and twisted and gyrated right in front of us, blowing a stream of bubbles in my face. Now the fun began! Up to four pups at a time came down to investigate us and then play with us before equally suddenly shooting up to the surface again for a gulp of air.

They somersaulted and pirouetted all around us, blew bubbles into our faces (they loved to surprise us with this trick!) and gently nibbled at our fins or even our outstretched fingers. They were amazingly gentle as they chewed softly away, seemingly enjoying having their silky smooth bodies stroked and staring into one's face with those huge, dark, liquid and unbelievably appealing eyes. They even barked underwater, sounding rather like a diver's air horn. What a fantastic introduction to the Sea of Cortez!

After such a magical experience at Los Islotes, we all wanted to go straight back, but our dive instructors said they knew best and we had to go to La Reina instead, as we were going to enjoy that even more. On the way out we came across a pod of 40 Common Dolphins that raced along in our bow wave or, whenever we slowed down, rolled lazily at the surface. After an hour La Reina hove into view, an isolated rocky outcrop just breaking the surface of the sea.

Mantas had been seen here regularly in recently weeks, but when we arrived and slowly circled the islet there were no tell-tale dark shadows moving under the surface, so we kitted up with a real sense of disappointment. Still, there was plenty to see, what with all those new fish, a huge Panamic Green Moray with a body as thick as a telephone pole and some tiny Panoramic Arrow Crabs sharing a hole with a sea urchin (yes almost everything around here is called Cortez-this or California-that, Pacific-this or Pacific that).

I was so distracted by this wealth of new creatures that the manta was almost on top of us by the time I looked up and saw an immense diamond-shaped creature slowly but inexorably approaching out of the murk. Straight towards us came this glory of the sea, and then it slowly turned to swim right alongside me, cephalic fins outstretched and tiny eyes following me calmly as I finned to keep up. As quietly as it had appeared it sailed away into the blue, all too soon for us! Time passed and the dive was nearing its end. We were ascending to our safety stop when a second manta appeared right behind Hilary. I caught her attention and she turned in time to gently stroke its 'wingtip' as it glided right past her. I felt a pang of envy, but then the manta turned, so gracefully for such a behemoth, and glided right at me, coming closer and closer as it climbed slowly until it glided right over my upturned face, showing every detail of its undersurface and accompanying remoras. I gently stroked its rough, sandpaper-like underside and its long whip-like tail - what a thrill to actually touch such a primordial creature! But even then the ballet had not ended, for the manta turned and came right past me yet again, virtually brushing its wingtip against me, before it made a third close pass and then slowly and seemingly reluctantly moved off, almost as if it was hoping for us to follow.

After all this, the dive at the Salvatierra car ferry wreck, interesting as it was, could only be an anticlimax. Surely nothing could rival the mantas that morning? We had not reckoned with the capacity of the Sea of Cortez in early autumn to amaze, however, and the show was by no means over. As we neared La Paz I was wondering why we were taking a different route into the bay when our divemaster casually said we were going to see if we could find a Whale Shark!

When we reached the head of the bay a couple of dive boats were already there, slowly following an immense adult Whale Shark that could be seen as a vast dark shadow below the surface, its dorsal fin occasionally breaking the surface. We waited our turn and then piled in. As the froth of bubbles cleared I was confronted by a huge, seemingly truck-sized snout and yawning mouth going right past me, followed by a wall of whitish spots, a big dorsal fin and a massive tail sweeping from side to side. Underwater the creature seemed so huge that it felt as if it was 30 meters long rather than just 10. The second time we went in with the mighty hulk we actually got pulled along in its slipstream like dolphins around a boat. What an incredible end to an already awesome day!

After all this, could there be more to come? Oh yes! Next morning we were anchored over El Bajo, a seamount summit far offshore. El Bajo is famous for its schooling hammerheads, but at some times of year, they are very deep, or unpredictable in their movements, or both. We were hoping October would turn up trumps. Down we went, following the anchor line into the rather murky depths. As we approached the top of the reef at around 25m the visibility started to improve dramatically and below 30m it was very clear.

However, as we swam 'downslope' towards an area favored by the hammerheads, it soon became apparent that a strong current was running and we were making slow progress. Down below us was a huge sunken tuna net draped over the flank of El Bajo, the 'signpost' to the realm of the hammerheads. I dropped to investigate and then suddenly they were there, 25 or 30 sinuous and powerful gray shapes moving to the left and away from us. We struggled to catch them, but soon realized it was hopeless in such a current. Heart rate and respiration were rising fast, but the sharks were gaining and slipping away into the gloom. How frustrating! So close and yet so far; it had all been over so quickly. As I rose towards the surface I knew we just had to try again. It was all a question of random chance, surely, and next time perhaps we would be in luck.

Our second visit to La Reina was even more wonderful than the first. As we swam along the border between the reef and the sandy flats we came across a vast school of Green Jacks, moving like a greyish-brown sandstorm across a desert until it enveloped us, shutting out most of the light. As the wall of fish began to thin, I realized that there was a huge shape coming towards us - yes, a manta was sailing along just behind the jacks like a huge aircraft that had emerged from behind a cloud.

Our final day saw us back at El Bajo again, ready for another visit to 'Hammerhead City'. This time it was soon obvious there was almost no current. Perfect! Now we were in with a real chance of close encounters. As we set off downslope a flash from one of the Japanese photographers from another dive boat alerted us, and yes there was the first Scalloped Hammerhead cruising along. I finned forward as fast as I dared at this depth and soon five or six were in clear view, with 20 more behind them.

Down below I could see several even bigger individuals, curving sinuously and exhibiting an immense but almost languorous power. We descended, leaving the Japanese party far behind, and below 40m these big 'guard individuals' were all around us, displaying those huge hammer-shaped heads and extraordinary beady eyes as they circled us in sinister perfection. Awesome! It was at this point, at 47m and with the air already feeling like treacle, that I realized there was something amazing going on out there. Yes, those close sharks had distracted me from the real spectacle, for as far as the eye could see there were hammerheads and hammerheads and hammerheads. It was hammerhead wallpaper out there . Could anything be more awesome than this?!

I could hardly drag myself away from such experiences, but I was well into deco and it was time to ascend. As I slowly moved towards the surface the last few hammerheads swept right underneath me and then, in seconds, they were gone as the crystal clear depths gave way to the murkier surface layers. I wanted to go back and join them.

I could go on and on and on about that week in the Sea of Cortez, not least the three (yes three!) Whale Sharks we snorkeled with that last afternoon, the pod of Short-finned Pilot Whales that dived right underneath me as I swam on the surface, the impressive Giant Hawkfish that made all those other hawkfish seem puny, and the amazing little Orangethroat Pike-Blennies. I think I had better have lowered expectations about the Sea of Cortez next time too: it would be tempting fate otherwise!