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Vessel-sourced sewage discharge restrictions in the Great Barrier Reef marine park and Torres Strait—advisory note

This advisory note provides guidance to coastal pilots about vessel-sourced sewage discharge restrictions in the Great Barrier Reef Marine Park (GBRMP) and Torres Strait.

AMSA acknowledges that adhering to these restrictions is the master’s responsibility, however it is understood that coastal pilots receive queries from masters and crew regarding the relevant discharge restrictions, from time to time. This PAN provides relevant information to assist coastal pilots when responding to such queries.


Vessel-sourced sewage discharge restrictions in Australian waters (including the GBRMP and Torres Strait) are established under Australian law. These laws give effect to Annex IV of the International Convention for the Prevention of Pollution from Ships (MARPOL). Marine Order 96 (Marine pollution prevention – sewage) 2013 (MO96) provides that a foreign vessel must comply with the requirements of Annex IV that apply to the vessel.

There are three main considerations related to discharges of vessel-sourced sewage:

  • the type of sewage treatment plant (STP) onboard (if any) and whether the plant has current IMO-approval and/or relevant certification
  • the type of sewage to be discharged (e.g. treated / comminuted* & disinfected / untreated), and
  • the distance from ‘nearest land’, where the discharge is intended to take place. *Comminute means to pulverize, to reduce to minute particles or fragments.

Nearest land 

MARPOL defines ‘nearest land’ to normally mean the territorial sea baseline (of the territory in question), however in the north-eastern part of Australia (including the Great Barrier Reef and Torres Strait), nearest land is defined by a series of specified coordinates. 

The MARPOL Nearest Land document provides visual maps of ‘nearest land’ for these regions. Note that the location of the ‘nearest land’ boundary in these areas: 

  • is seaward of the outer eastern edge of the Great Barrier Reef (GBR)
  • is generally aligned with the GBRMP boundary
  • encloses large parts of Torres Strait.

Maps depicting the nearest land boundary for the Torres Strait and the Inner Route pilotage areas are shown in Figures 1 and 2 below for reference purposes. 

Sewage Treatment Plants (STP’s)

STP’s may use biological, bioreactor, chemical, or membrane filtering processes, or a combination thereof, to achieve the minimum treatment standards (as specified by the IMO). Ship surveys undertaken by classification societies shall be such as to ensure that the structure, equipment, systems, fittings, arrangements and material fully comply with the applicable requirements of Annex IV to MARPOL. 

Vessels on international voyages 

In the case of vessels on international voyages (to and continuing in Australian waters), the discharge of effluent produced by an approved STP is permitted in the GBRMP and Torres Strait (with no restrictions related to the distance from nearest land), provided that: 

  • the STP is approved by the Administration^, taking into account the standards and test methods developed by the IMO~ (referred to in regulation 9.1.1 of MARPOL Annex IV), and
  • the discharge shall not produce any visible floating solids, nor any discolouration of the surrounding water when discharged.

Vessels that do not have an approved STP must have either a sewage ‘comminuting and disinfecting’ system onboard (approved by the Administration), with corresponding facilities for the temporary storage of the sewage, or a holding tank for untreated sewage. Under Australian law and MARPOL, vessel-sourced sewage effluent from these types of systems cannot be discharged anywhere within the GBRMP, nor anywhere enclosed by the ‘nearest land’ coordinates (including the relevant area within Torres Strait). 

‘Comminuted and disinfected’ sewage (generated using an approved system in accordance with regulation 9.1.2 of MARPOL Annex IV) is permitted to be discharged no less than 3NM from nearest land, provided that sewage originating from holding tanks, or sewage originating from spaces containing live animals, is discharged at a moderate rate while the ship is proceeding enroute at a speed not less than 4 knots. MO96 provides standards for the rate of discharge of such sewage. 

Untreated sewage can only be discharged at a distance no less than 12NM from nearest land, subject to the same discharge rate and vessel speed requirements described above for ‘comminuted and disinfected’ sewage. 

Further information about MARPOL’s vessel-sourced sewage discharge restrictions can be found on AMSA’s website (see Table 3 on the Summary of Discharge Standards page). 


^For the purposes of STP approval, ‘Administration’ means the Government of the State under whose authority the ship is operating. 

With respect to a ship entitled to fly a flag of any State, the Administration is the Government of that State. 

~Refer to the relevant information contained in the ‘Recommendation on International effluent standards and guidelines for performance tests for sewage treatment plants’, or in the ‘Revised guidelines on implementation of effluent standards and performance tests for sewage treatment plants’, adopted by the Marine Environment Protection Committee of the IMO.

Last updated: 14 April 2022