Diving in Darwin can at times be limited, due to tides and strong currents. Diving is only possible during neep tides, usually 6 to 8 days per month. Darwin Harbour does have some interesting dive locations, especially the World War 2 and Cyclone Tracy wrecks and is actually designated as one of the top 10 dive locations in the world.
The below link will take you to the NT tidal charts for dive times.
https://nt.gov.au/marine/for-all-harbour-and-boat-users/check-the-tides/tidal-information-nt-ports
We are currently working on this page with local Darwin information – we hope this will be complete shortly – in mean time feel free to contact us to get that not yet complete information. However in the mean time please use the Darwin Sub Aqua Club (DSAC) dive site page link as probably the best reference: