Koonya Inlet, south of Temma, is rated 6.5 out of 10 by the Marine Life Network guide as a sheltered shore dive with a patchy sand and rocky reef base that deepens towards the inlet mouth (about 10 m), where a weed garden holds interesting marine life. The shallows from 2 m suit beginners, numerous large abalone and crayfish in rock cracks are recorded, and the deeper reefs to 25 m are highly exposed, smooth-sided and swept clean, needing experienced divers with reserve air and good navigation. Access by four-wheel drive from Temma makes it a camping-trip destination. The Marine Life Network guide also describes the nearby wrecks of the SS Yolla (1898) and the SS Koonya (1919) near Sandy Cape, the latter a category-5 site it does not recommend.

Tasmania's west coast faces the full Southern Ocean, and the Marine Life Network guide notes that most of it is diveable only after easterly winds have flattened the swell - an uncommon event largely confined to summer. Macquarie Harbour and Cape Sorell provide the only reliable shelter from south-westerly swell. Crayfish grow large here, abalone are common and fish life is thin on exposed reefs, which are battered by constant swell.

There is no dive shop, air station or chamber anywhere on the west coast; the nearest hyperbaric chamber is the Royal Hobart Hospital, about 4 hours from Strahan by road. Every west coast dive should be treated as remote: carry oxygen, a radio and an EPIRB, and have a realistic evacuation plan.

Temma is about 45 km south of Arthur River on the gravel Western Explorer route. Koonya Inlet is reached by four-wheel drive from Temma - a major undertaking typically done as part of a camping trip. Enter in the sheltered inlet.

Roads south of Arthur River are gravel and there is no fuel between Arthur River and Zeehan, so carry spare fuel, water and a satellite communicator; mobile coverage is poor or absent on most of this coast.

The inlet is sheltered, but the deeper reefs outside are highly exposed to Southern Ocean swell. The prevailing westerly and south-westerly swell on this coast commonly exceeds 2-3 m; genuinely diveable days need several days of easterly or light winds and swell under about 1 m, which occur mostly from January to March. Rivers such as the Arthur and Pieman discharge dark tannin-stained water after rain, cutting visibility.

Dive the sheltered inlet from 2 m out to the weed garden at the mouth (about 10 m); only experienced divers with reserve air and navigation skills should head to the exposed outer reef. Turn at a third of gas to allow for the swim back and a possibly harder exit, finish with a 3-minute safety stop at about 5 m if the depth allows, and exit where you entered unless an alternative exit has been checked beforehand.

No dive operator on the west coast. Air and gear must come from Launceston, Burnie/Devonport or Hobart (the regional guide notes locals sent tanks overnight to Burnie for fills). Sites are dived only by self-sufficient private boats and abalone divers.