ITS NAME MAY NOT CONJURE UP FANTASTIC UNDERWATER IMAGES, like the Great Barrier Reef or the Galapagos, yet hidden beneath the stout old legs of a jetty in Western Australia is probably the most incredible riot of colour and variety of marine life that I have ever seen.
Busselton Jetty is like a buried jewel in the south-western corner of this huge continent. What marks it out as unique is that it stretches nearly 2km into the sea, and this is the reason for its profusion and range of life and colour.
Thanks to its location, it can take advantage of the Leewin Current, which brings a narrow band of warm water down the Western Australian coastline.
This current is responsible for introducing the diverse array of tropical and sub-tropical species that divers encounter here, and the growth of coral that is unusual at this latitude.
Busselton itself was named after its first European settler, John Garrett Bussell.
He arrived on the banks of the Vasse River in 1832. The track he cut from there to Geographe Bay is now Busseltons main street.
A pleasant seaside town 145 miles from Perth, it is located at the northern gateway to the Margaret River wine region and is a popular holiday destination for both Australians and international visitors.
The jetty, with its observatory, is now a major Western Australian eco-tourism attraction, and plays a large part in increasing the numbers of visitors to the area. Constructed in 1853 from giant karri hardwood, it is the longest wooden jetty in the southern hemisphere.
It was built to transport timber out of Geographe Bay, the inshore water being too shallow, and over the years was gradually extended until it reached its current length in the 1960s. A commercial railway line once ran the length of the jetty.

During the 60s state ships stopped using Busselton as a port of call, and the jetty was finally closed in 1971.
Rot set in, part of it caught fire and it was badly damaged during a cyclone. What funding could be found for repairs soon ran out. The Jetty Preservation Society was formed in 1987 to help raise funds for restoration work, and a small tourist train ran on the old tracks, divers using it to reach the end of the jetty.
This was stopped in 2005 because of concerns about deterioration of the jetty, and today the only way to access the magical world that lies beneath it is by boat.
Just over 1.8km from shore on the top of the jetty visitors can access the observatory, a room built on the seabed with large viewing windows and designed to accommodate 40 people.
Built in 2003, this allows people to view the fish from several metres under the sea. There is a no-swim zone around the observatory for divers, and in dive briefings you are asked to keep a certain distance away from the windows so that the fish arent scared away by your bubbles. Notices attached to the jetty legs remind you of this rule while youre diving, but tourists in the observatory seem to find it amusing to watch the divers, and usually give you a wave as you go by.
Its a 10-minute boat ride out to the jetty from the marina. Looking from the sea rather than the shore gives you a better idea of how incredibly long the jetty is, and how far it stretches out into the ocean. The boat moors up near the end of the jetty, the legs of which can often be seen as you descend the shot, and are merely a short swim away over the weed.
The depth varies only slightly with the tides, and is usually 7-8m.
Diving with local Busselton operator Peter from the Dive Shed, I soon became familiar with where the locals hung out, and where I was most likely to find particular fish. Even so, on every visit I saw much that was new to me.
As you leave the shotline and approach the legs of the pier, it looks as if someone has splashed the contents of a paintbox over them: colours of all hues seem to be present. Swimming on and under the first part of the jetty, you are often surrounded by the massive shoals of yellowtails that patrol this area.
With so much to see, I made a plan of which area I was going to investigate every time I dived here. It would be easy to get engrossed in taking photographs and never proceed further than the first 20m or so of one side!
Each jetty leg is a work of art, every centimetre smothered with sponges, ascidians and the telesto coral for which Busselton Jetty is particularly known. These are the bright orange fingers that stick out from the jetty legs, often covered with lacy white polyps. They open to filter the nutrient-rich water.
The bright pink of the rose sponge and translucent shades of blue-throated ascidians dominate the colour scheme in many places on the thick piles.
Tiny clingfish dart about. Globefish and brown-spotted wrasse lurk in the hollow pieces of broken jetty legs, while horseshoe leatherjackets and pineapplefish hide under those that have fallen over and lie on the seabed.
As you swim along the jetty towards the observatory, a small shoal of old wives will usually be swimming back and forth under the leaning legs.
The variety of marine life, too numerous to list, ranges from giant barnacles and cowfish to sea tulips and nudibranchs. Curious to see what the jetty was like from the other end, I joined a group diving it from the shore. For the first 50m or so there was little to view, then I started to see groups of common blowfish darting about, a few globefish idling around and the odd scorpionfish lying in wait on the bottom.
Gradually the jetty legs become coated, and then encrusted, with colourful life, leaving no sign of the original timbers. The seabed, with its broken legs and pieces of discarded debris, becomes a haven for numerous sea creatures while various fish busily pass by.
As more and more people discover the captivating world beneath this old jetty - its reputation is gradually growing.

Dive Shed Busselton offers a wide range of diving and training and can arrange accommodation, www.diveshed.com.au