Meet the site
The Denison Canal at Dunalley was cut through the narrow isthmus between Blackman Bay and Norfolk Bay in the early twentieth century to save coastal vessels the long voyage around the Tasman Peninsula, and it is still maintained for boat traffic today, with a swing bridge carrying the Arthur Highway. The Marine Life Network guide calls it the only easy drift dive in south-east Tasmania: the tidal stream through the canal can be fast, carrying divers along the muddy bottom at about 10 m. Schools of soldier fish (a local name, probably for bullseyes or cardinalfish) shelter along the canal walls, and in season spider crabs gather in mating congregations – an extraordinary spectacle when hundreds or thousands of crabs pile on top of each other. The bottom is mud with scattered debris, and there are the usual estuarine species such as flathead, sea stars and small crabs. The dive is strictly controlled: the guide says divers need Harbour Master permission and a manned safety boat that follows and picks them up, because the canal is an active navigation channel. Visibility is usually modest. For a group with the right arrangements, the canal provides a fun and unusual dive. Without them, it should not be attempted. Dunalley has a pub, cafe and bakery, and makes a convenient stop on the way to the Tasman Peninsula. Divers interested in the site should contact TasPorts or Marine and Safety Tasmania well in advance, and dive with a club that has done it before. Spider crab aggregations elsewhere in southern Australia typically occur in late autumn and winter, so ask locally about timing.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Dunalley (Denison) Canal is recorded as Drift in Tasman Peninsula. The listed access is boat (day trip). 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.
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 Dunalley (Denison) Canal suitable for my certification?
The record lists Advanced 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 Dunalley (Denison) Canal 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
Spider crabs (seasonal aggregations), schooling 'soldier fish' (cardinalfish/bullseyes), flathead, sea stars, crabs, estuarine fish
Location
Narrow man-made canal through the isthmus at Dunalley linking Blackman Bay and Norfolk Bay, dived as a tidal drift.
Facilities nearby
Dunalley boat ramp, pub, cafe and bakery; fills in Hobart.
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
marinelife.org.auRecord updated 26 Sept 2026. Source claims are being reviewed.