Castle Rock is a reef and pinnacle site located off Portsea, Australia. The topography features a wall and reef structure at depths between 12 and 20 metres. This site is defined by strong tidal currents flowing through Port Phillip Heads, necessitating dives timed strictly for slack water. Visibility typically ranges from 5 to 15 metres. Due to the challenging currents and potential for significant swell, this site is suitable only for advanced divers. Water temperatures fluctuate between 13C and 19C, making a 7mm wetsuit or drysuit essential. Boat access is required for all dives, which generally last around 45 minutes.

The HMAS J4 is an upright submarine wreck resting at a depth of 26 to 27 metres off Portsea. This boat-access site is suited for advanced divers due to frequent strong currents and surge. The hull is heavily encrusted with kelp and seaweed. Visibility typically ranges between 5 and 15 metres. Due to the risk of entanglement and potential for silt-out, penetration is hazardous. Divers should plan their visit around slack water to manage the challenging conditions. Species recorded around this area include weedy seadragons, giant cuttlefish, western blue devils, and various wrasse species.

The SS Coogee is a wreck dive situated in the treacherous entrance to Port Phillip Bay known as The Rip. Resting at depths between 29 and 35 metres, this site is strictly for advanced divers due to extreme tidal currents that can exceed 6 knots. Diving must be conducted exclusively during slack water to ensure safety. Visibility ranges from 4 to 25 metres, with the best conditions typically occurring during the winter months. Access is by boat only, located 4 kilometres from shore. Given the depth and the potential for strong currents, divers should plan for decompression and use a local charter operator familiar with the specific tidal windows.

The HMAS J5 is a submarine wreck resting upright on the seabed at depths between 30 and 36 metres. This advanced dive requires boat access and is subject to moderate currents of 1 to 2 knots, which can funnel through the structure. Visibility typically ranges from 5 to 10 metres. The wreck features an overhead environment with tight internal spaces, making penetration hazardous due to potential silt-out and structural deterioration. Divers should be prepared for water temperatures between 13C and 18C. Given the depth and conditions, redundant air sources and multiple lights are mandatory for those planning to explore the interior of the hull.

The HMAS J2 is a decommissioned Royal Australian Navy submarine resting upright on the seafloor at depths between 37 and 39 metres. Located 3000 metres offshore, this wreck is a deep dive site requiring boat access. The hull is broken in two places, with a collapsed section behind the conning tower. Due to the risk of fine silting and disorientation, penetration is not recommended. Divers should be prepared for cold water temperatures, potential low visibility, and boat traffic as the site lies within a shipping lane. This site is suitable for advanced divers with wreck experience who can manage decompression requirements and overhead environments.

Lonsdale Arches is a boat-access reef and cave system located in Port Phillip Heads. The site features arches and cave structures at depths ranging from 10 to 18 metres, with an average depth of 14 metres. Visibility typically spans 10 to 15 metres. This site is exposed to strong tidal currents from Port Phillip Heads, making it essential to dive only during slack water to avoid being swept away. Due to the proximity of the shipping channel, boat traffic is a constant consideration. Water temperatures range from 13C to 19C, necessitating a 7mm wetsuit or drysuit. The site is suitable for intermediate divers.

The HMAS Canberra is a decommissioned warship resting upright on a sandy bottom near Portsea. The wreck offers a range of depths from 12 metres at the superstructure to 33 metres at the hull, requiring advanced buoyancy and gas management skills. Divers access the site by boat, and the wreck features multiple entry and exit points for penetration. Conditions vary, with moderate currents and surge common; the site is best dived during slack tide in calm weather. Visibility typically ranges between 6 and 15 metres. Due to water temperatures between 13C and 18C, a 7mm wetsuit or drysuit is recommended for the average 40-minute dive.

The HMAS J1 submarine is an artificial reef resting on the seabed at a depth of 35 to 36 metres. Located 4500 metres from shore near Port Phillip Heads, this wreck is a challenging dive suitable only for advanced divers. The site is subject to strong currents, requiring dives to be carefully timed for slack water. Visibility typically ranges from 10 to 20 metres. Due to the depth, cold water temperatures between 13C and 18C, and the risks associated with the overhead environment, this site demands careful decompression planning and appropriate thermal protection. Boat access is required, and guided tours are recommended for navigating this historic wreck.