The impression by the time we descend towards LAX airport is that everything has grown larger than life.

Very loud passengers have surrounded our small British enclave and, like besieged homesteaders, we cower in our corner of the plane. But, as you soon discover when you visit the USA, most Americans just want to be friendly.

I have been looking forward to flying west for a change. From Los Angeles, we are soon on an extremely fast ferry heading for the Channel Islands. Catalina reminds me of the vintage TV series The Prisoner, in which everybody travelled around by golf-cart, the buildings were perfect and not a blemish was to be seen. Los Angelenos wander through the gift shops, and diners fill the sea-front restaurants, devouring 12oz steaks with double fries. The atmosphere is one of wholesome beachside Americana.

Captain Bob Kennedy is a larger-than-life character. He is there to take us to sea every day in his well-appointed dive boat Catalina Scuba Luv, alternating between the kelp forests just off the island one day, and further out to sea to find blue sharks the next.

The vessel is large, wide and stable. The crew prepare fine lunches for us each day, and any kind of soft drink is available through a dispenser.

You can leave your kit safely aboard at the end of each day, and opposite our hotel is an earthy sports bar full of baseball-loving locals which, of course, becomes our default meeting place after each days diving.

Forests of 30m-long kelp fronds tower to the surface within a few hundred metres of Catalina island. Descend through these forests and look upwards and the light seems to explode in your eyes. The sunbursts battle to penetrate these Pacific waters to the seabed creates an eerie atmosphere. Garibaldifish abound in the kelp. They dart around and pose for the camera as confidently as any fish I have seen.

Harbour seals swim in to investigate us, quick as a flash and, in the lowered visibility, without warning. This welcome surprise occurs on two of the three days we spend diving the kelp forests.

But the other three days we spend looking for blue sharks. These trips vary from one to three hours, and see us steaming around leaving a trail of fish guts in the water.

For the first two days we have little success, but on the last day of our trip, we get lucky.

Once we have started to spot the blues, the cage is lowered into the water and the chum dispensed in greater quantities. Three divers are allowed into the water outside the cage at one time so that no one will be crowded out, and this includes one of the experienced crew-members, but the cage is available to anyone wishing to use it. Two lengths of rope are attached to it, as there is a strong current, and these help to provide me with some stability in the water while holding the camera.

Small and medium-sized blue sharks buzz us all day as they consume the chum. Sleek and attractive but also confident, they make great photographic subjects. They approach us slowly and appear not in the least bit unnerved by our presence, which gives the poorest of underwater photographers time to focus.

They circle us from above and below and my only worry is how much air I have left. I really dont want to miss any of the spectacle.

In among the blues, mako sharks then start to swim in at high speed. This adds another dimension to the excitement - you have to be very quick to spot them approaching, especially with the visibility down, as it is today.

Most of the sharks we see are young ones, but diving with these pelagics is a memorable experience.

You buy into an all-American experience when you dive at Catalina Island and it is an enjoyable one, from Captain Bob whooping on the bridge of his boat to the massive burgers back on dry land.

Catalina has a lot to offer non-divers and divers alike, but it is the scuba diver who will get the best of it.

- Dive centre and resort Catalina Scuba Luv is the largest operation on Catalina, and is open year-round. It can arrange dive packages to the island including ferry, hotel accommodation and diving, and a number of speciality trips and courses. Shark trips cost $239 per person. www.scubaluv.com

The Catalina Scuba Luv dive boat
Blue sharks are a spectacular sight in the blue, even more so in the eerie kelp forests.
A blue shark in the kelp.
Garibaldifish are a familiar forest sight
Take your pick - stay inside the cage or hang out outside to photograph it