The Betsey Island graveyard, west of Little Betsey Island at the mouth of the Derwent, is Hobart's ships' graveyard: from the 1930s to the 1980s obsolete vessels, barges and sections of the old floating bridge were towed here and scuttled in about 20-34 m. The Marine Life Network guide calls it a huge concentration of wreck dives very close to Hobart, with a pebble-and-mud bottom that stirs up easily, poor visibility after bad weather or decaying Storm Bay swell, and massive yellow and white jewel anemones and, at times, hordes of school fish on the wrecks. The William Cowper was built in Holland in 1924 and ended her career in Hobart.

According to the guide she was scuttled here in 1979 after a failed contract to dump jarosite waste from the Risdon zinc works; she was 689 tons and 170 ft (52 m) long. Today she lies about 100 m west of Little Betsey Island, oriented west to east, in about 20 m. The hull has flattened over the decades, so rather than an upright ship divers find a spread of plates, frames and machinery that makes an easy linear navigation along the wreck's axis.

Like the other graveyard wrecks, the steel is covered in jewel anemones and encrusting invertebrates, and schools of fish shelter in the gaps. Crabs, octopus and small fish hide among the plates, and larger fish sometimes cruise over the site. The wreck's link to the jarosite dumping era is an interesting footnote in Hobart's industrial history: for years, waste from the zinc works was dumped at sea off Tasmania before the practice ended.

Expect low visibility and a silty bottom that clouds with careless fin kicks. This is a straightforward wreck dive for Advanced divers comfortable in poor visibility, and it is easily combined with the Macquarie or the barges nearby.

South Arm is about 35 km (40 minutes) south-east of Hobart: cross the Tasman Bridge, follow the South Arm Highway (B33) through Rokeby and Lauderdale to South Arm. The main boat ramp is at South Arm (Blessington Street/Harbour area) with trailer parking and toilets; Lauderdale (Doran's Road) is an alternative ramp further north. From South Arm the Betsey Island graveyard lies about 5-6 km south-east across the mouth of the Derwent, west of Little Betsey Island, roughly 15-20 minutes by boat.

The Marine Life Network guide recommends an echo sounder to locate the individual wrecks, which are low on the bottom; there are no public moorings, so anchor carefully in the pebble-mud bottom off the wreck and leave a boat attendant.

Betsey Island lies at the mouth of the Derwent where it meets Storm Bay, so decaying southerly swell and strong southerly or south-westerly winds make the ride rough and stir up the pebble-and-mud bottom. The Marine Life Network notes the graveyard is not renowned for visibility and recommends calm, dry weather and an ebb tide, when clearer water sits over the wrecks. After Derwent floods the water can be very dark.

Northerly and light westerly winds give the best conditions; late summer and autumn are most reliable. Expect 3-8 m visibility at best, often less.

Drop a shot at the western end of the hull, follow the flattened wreck east along its length at 20 m, and return to the shot. Use a reel if visibility is below 3 m.

No scheduled operator trips; Hobart clubs (Tasmanian Scuba Diving Club and others) and private boats from South Arm and Lauderdale. The Dive Shop Hobart and Go Dive Tasmania can advise.