Ruling the waves – regulating Australia’s offshore waters

Legal briefing 116 1 December 2020
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The measuring point – the territorial sea baseline
International law 
Under UNCLOS, the outer limits of all the maritime zones (other than the high seas 
and the Area) are measured from the territorial sea ‘baseline’. UNCLOS sets out several 
methods for determining the baseline. Under Art 14 of UNCLOS, each coastal nation is 
able to determine its own baseline in accordance with these methods.
Article 5 of UNCLOS provides that the ‘normal baseline’ is 
the low water line along the coast as marked on large-scale 
charts officially recognised by the coastal nation. Important 
exceptions to this general rule permit straight baselines to 
be drawn (UNCLOS, Arts 7, 9 and 10):
• across the mouths of certain bays and rivers
• between the mainland and adjacent islands in some 
circumstances.
A baseline may be drawn for any coast in the relevant 
nation. For Australia, this includes the coast on the mainland, islands, and uninhabited 
rocks.
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Australian law
Under Australian law, the Governor-General is empowered under s 7(1) of the SSL Act 
to declare by proclamation the limits of the whole or of any part of the territorial sea. 
Section 7(2)(b) of the SSL Act permits the Governor-General to determine the baseline 
from which the breadth of the territorial sea, or of any part of the territorial sea, is to be
measured.
The principal proclamation is the Seas and Submerged Lands (Territorial Sea Baseline) 
Proclamation 2006. Under that proclamation, the baseline is the low water line, except 
where a straight baseline may be drawn according to the principles set out in UNCLOS.
As a result, where the baseline is the low water line, its location moves with changes 
in the physical characteristics of the coastline and adjacent islands. For example, if a 
beach erodes or an island becomes submerged, the location of the baseline will shift 
accordingly.