The jetty was completed in 1860 and once stretched 652 m; storm damage in the mid-1930s shortened it to its present length of about 585 m, as repairs were considered unaffordable during the Depression. A First World War memorial clock stands at its landward end, and the jetty hosts the annual Kite and Greek festivals. According to fishing guides, the jetty sits over a shallow sandy bottom, with some broken ground at the end, and its piles hold bream.

That suggests a shallow, largely sandy dive with limited reef structure except near the outer end. Pile growth of algae, sponges and ascidians, and the life it attracts – small fish, crabs, octopus and cuttlefish, especially at night – are likely, but not documented by divers. Practically, Semaphore is a long swim for limited reward compared with Port Noarlunga or the Yorke Peninsula and Fleurieu jetties, and visibility along this coast is often poor.

It may still appeal to local residents as a calm-day snorkel, a night dive close to home, or an exploratory dive for photographers interested in recording what lives on Adelaide's lesser-known jetties. Divers should expect busy fishing activity and keep well clear of lines, and should be conscious of the swimming area and events near the jetty head. Reports of what is found would be welcomed by the Scuba Divers Federation of SA.

Semaphore is about 25 minutes north-west of the Adelaide CBD. Park along the Esplanade near the jetty and Semaphore Road (free, busy on summer weekends and festival days). Enter from the beach beside the jetty and snorkel out along the piles; the more interesting broken ground is near the end, a long surface swim of over 500 m, so many divers content themselves with the outer third.

There are no documented diver stairs. Gear up at the car and walk across the sand; the carry is short. Swim out on the surface with a torch and surface marker buoy, and stay beside or under the jetty rather than out in the swimming area.

Entry and exit through small shore-break waves is easiest at mid to high tide.

These northern metro jetties sit on a shallow, sandy, west-facing coast. They are only worth diving in flat conditions after several days of easterly (offshore) winds; any westerly or south-westerly wind or swell stirs up the sand and turns the water milky, and the summer sea breeze usually arrives by early afternoon. The tidal range is small, but low tide leaves little water under the inshore half.

Visibility falls sharply after rain because of stormwater and river outflow along the coast. Night dives on calm evenings give the best chance of cephalopods.

Enter from the beach beside the jetty, snorkel out to the deeper outer half, then descend and work slowly along the piles with a torch, keeping well clear of fishing lines. Return along the other side and exit on the beach.

No dive operator uses this jetty; nearest shops for fills and advice are in Glenelg (Adelaide Scuba, The Dive Shack) and Edwardstown (Underwater Sports).