Off Coombe Reserve, the Swan River channel drops to more than 20 m, and two wrecks lie in 19–22 m. Howies Scuba, whose writer dived only one of them, describes the water as black as night and thick as tar, and Howies' site table calls it a dark, cold, murky hole in a working river, with visibility of about half a metre. It requires Advanced training and a torch.

The wrecks are unidentified boats, part of the seven wrecks Divingwawrecks records at the Coombe. Little is published about their size or condition. Their appeal lies in the challenge: a deep, dark river dive that tests buoyancy, navigation and composure. Marine life is sparse, mostly encrusting growth, anemones and small fish.

The site is reached by a 250 m surface swim to mooring buoy 352 or a tide-dependent shoreline walk to buoy 107. The surface swim crosses water used by boats and water skiers, and the channel carries tidal currents, so timing and a flag are essential.

This is a dive for experienced divers with Advanced or deep training, good torches and a buddy they trust, ideally with previous experience of the shallow Coombe wrecks. For most divers the shallow wrecks, Bicton Baths or Blackwall Reach give a better river experience with less risk.

River temperatures swing more than the ocean: about 22–26 °C in late summer but as low as 13–15 °C in winter, when a 7 mm suit or drysuit makes a long dive more comfortable. Rinse gear well afterwards, as the estuary water is often high in organic matter.

Park at Coombe Reserve on The Coombe, Mosman Park (space for about 10 cars) and kit up on the grass. Swim about 250 m out to mooring buoy 352 and descend there, or, depending on the tide, walk along the shoreline to buoy 107 and descend from closer in. Tow a flag on the surface swim, as boats use this reach.

About 10 minutes from Fremantle.

Unaffected by ocean swell but strongly affected by the tide and river conditions. Currents are strongest in the channel, so dive at slack water on neap tides. Visibility is often below 1 m and can be close to zero, especially after rain or dredging.

Water at depth is cold and dark in winter.

Descend the mooring line to the bottom at about 20 m with torches on, locate the wreck close to the mooring, explore it briefly within no-decompression limits and ascend the same line.

Plan conservatively; consider a reel and a buddy line in near-zero visibility.

No operator; experienced local divers only.