Meet the site
Lonsdale Arches is the showpiece of the outer Lonsdale reef. About a kilometre from Point Lonsdale light on the Bass Strait side of the Heads, the sandstone reef has been 'carved into intricate structures including arches and tunnels', in the words of the Scuba Doctor listing, which calls the site spectacular and notes 'a couple of amazing swim-throughs that are very safe and easy to enter'. The depth is a comfortable 12–18 m, and the whole reef can be covered in a 40-minute dive.
The arches are natural bridges where the current has bored through ridges of rock, big enough to swim through in a relaxed horizontal position with light visible all the way; the tunnels are longer but still open at both ends and free of silt. What lifts them above ordinary swim-throughs is the growth: the strong tidal flow through the entrance creates 'a nutrient-rich environment and subsequently prolific marine growth', and the undersides of the arches are solid with yellow zoanthids, jewel anemones, orange sponges and bryozoans. Southern blue devils, magpie perch, silver sweep and longsnout boarfish are the regular fish; southern rock lobster, giant Australian cuttlefish, draughtboard sharks and Port Jackson sharks are common, and Australian fur seals from the nearby haul-outs often follow divers through the arches.
It is dived on the ebb – the outgoing tide leaves this side of the reef in relatively slack water – and the limit is swell rather than current, since the site is fully exposed to Bass Strait. On a calm day it is an easy, memorable Open Water dive and one of the most photographed sites in Victoria; Twin Bommies, Lonsdale Bommies and Castle Rock lie on the same reef and are commonly combined with it on an 'outside' charter day.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Lonsdale Arches is recorded as Reef in Port Phillip Heads. The listed access is boat. Confirm the actual meeting point, route and permission to visit; a map pin does not establish any of these.
Topics flagged by the stored research
These are questions prompted by the existing notes, not a verified or complete hazard assessment.
- Current and timing
- Ask how the operator assesses the current window for the actual route. Historical tide notes are not a departure instruction.
- Other water users
- Ask about vessel activity, exclusion areas and the agreed surface arrangements.
- Water movement
- Ask how swell and local exposure affect the proposed entry, exit and route.
Historical access notes exist for this record, but have not been independently verified for current use. Request current directions from the operator or site manager rather than following an old entry description.
Questions, answered
Is Lonsdale Arches suitable for my certification?
The record lists Open Water. That does not establish suitability for every route or day. Share your training, recent experience and equipment needs with the operator and ask about the specific proposed dive.
Can I book Lonsdale Arches through YouDive?
YouDive is an independent research directory. Contact an operator directly to confirm whether it currently runs the trip, the inclusions and the booking terms.
What you might see
Southern blue devil, magpie perch, silver sweep, longsnout boarfish, southern rock lobster, giant Australian cuttlefish, draughtboard shark, Port Jackson shark, Australian fur seal, yellow zoanthids, jewel anemones, sponges, bryozoans
Location
Outside the Heads in Bass Strait, about 1 km south-south-west of Point Lonsdale lighthouse on the outer Lonsdale reef; 83 m from Twin Bommies and 200 m west of Lonsdale Bommies.
Before you make plans
Conditions, access and operator schedules can change. This is a location guide, not a dive plan. Ask a local operator about current conditions and suitability for your training and experience.
Sources & further reading
scubadoctor.com.auparks.vic.gov.auscubadoctor.com.auRecord updated 26 Sept 2026. Source claims are being reviewed.
