Maritime environmental compliance is no longer a narrow technical issue handled only by the engine room, the superintendent, or the class desk. It is now a core legal and commercial duty for shipowners and operators because environmental rules affect whether a ship can trade, what fuel it can burn, what records it must keep, which certificates it must carry, how it manages ballast water and waste, how it is inspected in port, and, increasingly, how much it pays for carbon-related compliance. At the global level, the legal framework is built first on MARPOL, which IMO describes as the main international convention covering prevention of pollution of the marine environment by ships from operational or accidental causes. MARPOL currently has six technical Annexes dealing with oil, noxious liquid substances in bulk, harmful substances in packaged form, sewage, garbage, and air pollution from ships.
For shipowners and operators, the practical significance of this framework is straightforward. Environmental compliance is not only about avoiding spills. It is also about routine operational compliance: fuel sulfur content, sewage discharge controls, ballast water treatment, anti-fouling systems, garbage handling, energy-efficiency planning, carbon-intensity reporting, and end-of-life recycling preparation. On top of the IMO framework, regional regimes now matter more than ever. In the European Union, maritime transport is already inside the EU ETS, and FuelEU Maritime is in force for ships above 5,000 gross tonnage calling at EU ports, regardless of flag. That combination means environmental compliance has become a full-lifecycle legal obligation, from design and certification to operations, port calls, and recycling.
The Core Legal Framework
The starting point remains MARPOL. IMO states that the convention includes regulations aimed at preventing and minimizing pollution from ships from both accidental pollution and routine operations. Annex I deals with oil pollution, Annex II with noxious liquid substances in bulk, Annex III with harmful substances in packaged form, Annex IV with sewage, Annex V with garbage, and Annex VI with air pollution and energy-efficiency measures. These annexes are not abstract environmental goals. They are the legal source of concrete owner and operator duties, including equipment requirements, discharge restrictions, recordkeeping, surveys, and certification.
The second layer is made up of specialized conventions that address environmental risks outside or alongside core MARPOL discharge control. The Ballast Water Management Convention entered into force on 8 September 2017 and applies to ships that take up and use ballast water during international voyages. The Anti-Fouling Systems Convention entered into force on 17 September 2008 and prohibits harmful organotins while providing a mechanism to control future harmful substances in anti-fouling systems. The Hong Kong Convention on ship recycling entered into force on 26 June 2025 and requires ships to carry and maintain an Inventory of Hazardous Materials and to be recycled only at authorized facilities in states party to the convention.
A third layer now comes from climate regulation. IMO’s 2023 GHG Strategy includes a target to reduce the carbon intensity of international shipping by at least 40% by 2030 compared with 2008, to increase the uptake of zero or near-zero GHG fuels or energy sources to at least 5%, striving for 10%, by 2030, and to reach net-zero GHG emissions from international shipping by or around 2050. That strategic direction is already reflected in mandatory MARPOL Annex VI measures such as EEXI, CII, and the enhanced SEEMP framework.
The Shipowner’s Baseline Legal Duty
At a legal and operational level, the owner and operator’s first duty is not simply to react to environmental rules when port State control arrives. It is to build a compliance system that matches the ship’s trading pattern, tonnage, fuel profile, equipment, and certificates. That system normally includes valid statutory certificates, ship-specific plans, record books, survey readiness, documentary traceability, and internal operating procedures. IMO’s 2025 Port State Control Procedures list environmental documents that may be checked in inspection, including the International Oil Pollution Prevention Certificate, International Sewage Pollution Prevention Certificate, International Air Pollution Prevention Certificate, International Energy Efficiency Certificate, International Ballast Water Management Certificate, and International Anti-fouling System Certificate.
That document-heavy structure matters because maritime environmental compliance is enforced through paper as much as through hardware. A ship may physically be equipped to comply, but a missing or invalid certificate can still become a detainable deficiency. IMO’s 2025 PSC Procedures specifically identify the absence of a valid International Air Pollution Prevention Certificate, International Energy Efficiency Certificate, SEEMP, and International Anti-fouling System Certificate as inspection deficiencies, and they also recognize ballast-water and sewage certificate deficiencies as PSC concerns. In practice, that means the legal duty is twofold: comply substantively and prove compliance documentarily.
MARPOL Annex I: Oil Pollution Prevention
Annex I is the oldest and still one of the most commercially important pollution-control regimes. IMO states that Annex I covers prevention of pollution by oil from operational measures as well as accidental discharges, and that later amendments made double hulls mandatory for new oil tankers and phased them in for existing tanker fleets. For owners and operators, the broader legal lesson is that oil pollution compliance is not limited to catastrophic spills. It includes day-to-day operational control of oily residues, sludge, machinery-space discharges, and cargo-related oil management.
Annex I also anchors a large part of the certification and recordkeeping burden. IMO’s 2025 PSC Procedures list the IOPP Certificate among the core environmental certificates subject to inspection. Ballast water compliance scheduling is also linked in part to the ship’s IOPPC renewal survey, which shows how MARPOL Annex I documentation influences other environmental regimes. For shipowners, that means Annex I compliance is not siloed; it often acts as a documentary backbone for wider environmental oversight.
MARPOL Annexes II and III: Chemicals and Packaged Harmful Substances
Annex II addresses noxious liquid substances in bulk and, according to IMO, sets discharge criteria and control measures for roughly 250 evaluated substances. IMO’s MARPOL summary notes that discharge of residues is permitted only to reception facilities until the required concentration and handling conditions are met, and in any event no discharge of residues containing noxious substances is allowed within 12 miles of the nearest land. For chemical tanker operators and anyone carrying Annex II cargoes, environmental compliance therefore depends not only on pollution prevention equipment, but also on cargo classification, tank-wash management, and reception-facility planning.
Annex III deals with harmful substances carried in packaged form and sets general requirements for packing, marking, labelling, documentation, stowage, quantity limitations, exceptions, and notifications. IMO links the concept of harmful substances in Annex III to marine pollutants identified in the IMDG Code or meeting the criteria in the Annex’s appendix. For owners and operators, this means environmental compliance in packaged-goods trades is closely tied to cargo-documentation accuracy and dangerous-goods compliance, not just discharge rules.
MARPOL Annex IV: Sewage
Annex IV is often underestimated by commercial operators, but it imposes concrete equipment and discharge duties. IMO states that the revised Annex IV applies to ships on international voyages of 400 gross tonnage and above or ships certified to carry more than 15 persons. Such ships must be equipped with either an approved sewage treatment plant, an approved comminuting and disinfecting system, or a sewage holding tank. Discharge of raw or untreated sewage is prohibited except under specific distance, treatment, and operational conditions. Governments are also required to ensure adequate port reception facilities for sewage.
For shipowners, the legal duty under Annex IV is therefore not only to avoid illegal discharge, but also to ensure that the vessel’s sewage system, certification, and operational procedures remain aligned. IMO’s PSC framework treats absence of a valid International Sewage Pollution Prevention Certificate and failure of sewage treatment equipment as inspection issues. That means sewage compliance can create both environmental liability and immediate port-state-operational risk.
MARPOL Annex V: Garbage and Port Reception
Annex V is one of the clearest examples of routine operational environmental compliance. IMO states that Annex V generally prohibits the discharge of all garbage into the sea, except for the narrow categories expressly permitted by regulations 4, 5, and 6. It also states that the Annex applies broadly to all ships and that plastics have been banned from discharge since 1988. In addition, ships of 12 metres or more must display placards, and ships of 100 gross tonnage and above, ships certified to carry 15 persons or more, and fixed or floating platforms must carry a garbage management plan.
This is where owner and operator conduct matters daily. Garbage segregation, onboard handling, delivery to reception facilities, recordkeeping, and crew awareness are all part of compliance. IMO also emphasizes that the effectiveness of Annex V depends on adequate port reception facilities, and it reminds parties to Annex V that they must provide such facilities without causing undue delay to ships. That means a shipowner cannot simply claim operational necessity as a reason for improper disposal; the legal system expects both ship-side procedures and shore-side reception planning.
MARPOL Annex VI: Air Emissions and Energy Efficiency
Annex VI is now one of the most commercially significant environmental regimes. IMO states that Annex VI sets limits on sulfur oxide and nitrogen oxide emissions, prohibits deliberate emissions of ozone-depleting substances, and includes mandatory technical and operational energy-efficiency measures. Outside designated emission control areas, the global sulfur cap has been 0.50% m/m since 1 January 2020; within sulfur ECAs the limit is 0.10% m/m. IMO also confirms that the Mediterranean Sea became a sulfur ECA on 1 May 2025, meaning ships in the area must now comply with the 0.10% sulfur limit there as well.
For shipowners and operators, Annex VI compliance is both technical and procedural. The owner must ensure compliant fuel or an equivalent approved method, maintain valid air-pollution certification, and operate the ship consistently with the sulfur rules on both use and carriage of fuel oil. IMO notes that from 1 March 2020 MARPOL also prohibits carriage for onboard use of fuel oil above the global sulfur limit unless the ship uses an approved alternative compliance method, which means bunker procurement, segregation, and sampling practice are all legal-risk areas.
Annex VI now also includes the short-term GHG measures. IMO states that the amendments for EEXI and CII entered into force on 1 November 2022, with certification requirements taking effect on 1 January 2023. All existing ships of 400 GT and above must calculate attained EEXI, and ships of 5,000 GT and above must calculate and report annual CII performance. Ships are rated A to E, and a ship rated D for three consecutive years or E for one year must develop a corrective action plan. IMO also explains that the SEEMP now has three parts: a ship management plan to improve energy efficiency, a fuel-oil data collection plan, and a ship operational carbon-intensity plan.
Ballast Water Management
The Ballast Water Management Convention is one of the clearest examples of an owner/operator compliance regime that combines equipment, records, certificates, and port-state inspection. IMO states that the convention entered into force on 8 September 2017 and applies to ships registered under contracting parties that take up and use ballast water during international voyages. Ships must manage ballast water and sediments to the required standard under a ship-specific ballast water management plan. They must carry a ballast water record book and, for ships of 400 GT and above, an International Ballast Water Management Certificate.
The compliance burden is substantive as well as documentary. IMO explains that the convention uses the D-1 ballast water exchange standard and the D-2 ballast water performance standard, with D-2 phased in for existing ships and fully applicable by 8 September 2024. Port States may verify the certificate and approved plan, inspect the ballast water record book, and sample ballast water. For owners and operators, that means ballast-water compliance is a recurring operational obligation, not a one-time installation decision.
Anti-Fouling and Hull Compliance
The AFS Convention adds another layer of environmental duty. IMO states that the convention prohibits harmful organotins in anti-fouling systems and creates a framework for controlling future harmful substances in those systems. Parties must restrict such coatings not only on ships flying their flag, but also on ships entering their ports, shipyards, or offshore terminals. This makes anti-fouling compliance both a flag-state and port-state issue.
IMO’s 2025 PSC Procedures list the International Anti-fouling System Certificate or a Declaration on AFS among the environmental documents subject to inspection, and they identify missing or invalid AFS certification as a deficiency. The same PSC procedures also show that non-compliance with AFS rules can lead to detention, dismissal from port, or an order to proceed elsewhere for rectification if sampling or admissions show non-compliance. For owners and operators, anti-fouling compliance is therefore no longer a purely maintenance or dry-docking topic. It is also a legal-access and inspection-risk topic.
Ship Recycling and End-of-Life Compliance
Environmental compliance now extends to the end of the ship’s life. IMO states that the Hong Kong Convention entered into force on 26 June 2025. Under that convention, ships must have on board an Inventory of Hazardous Materials specific to the ship, and that inventory must be prepared, verified, kept up to date, and supported by initial, additional, and final surveys. Ships flying the flag of a party to the convention may be dismantled only at authorized ship recycling facilities that meet the convention’s standards.
This is a major change in owner and operator responsibility. Ship recycling is no longer only a commercial disposal issue. It is now a regulated environmental compliance field that reaches back into ship operation and document management long before demolition. Owners need to treat hazardous-material inventory management as part of lifecycle compliance, especially if the ship is likely to trade under the flag of a party to the convention or to be recycled under that framework.
The EU Overlay: ETS and FuelEU Maritime
For ships calling at EU ports, global IMO compliance is no longer enough. The European Commission states that the EU ETS has covered maritime transport since January 2024 for large ships of 5,000 GT and above entering EU ports, regardless of flag. The phase-in requires shipping companies to surrender allowances for 40% of emissions reported for 2024 in 2025, 70% of emissions reported for 2025 in 2026, and 100% from 2027 onward. The first surrender deadline fell in September 2025 for 2024 emissions.
FuelEU Maritime adds a second EU climate layer. The Commission states that Regulation (EU) 2023/1805 promotes renewable and low-carbon fuels and clean energy technologies for ships. It also states that the regime applies to ships above 5,000 GT calling at EU ports, regardless of flag, and requires a gradual reduction in the GHG intensity of energy used on board, starting at -2% in 2025 and increasing to -80% by 2050 compared with the 2020 baseline. By April 2026, the Commission had already published several implementing and delegated acts supporting verification, monitoring plans, verifier accreditation, and FuelEU database functionality.
For owners and operators, the legal effect of this EU layer is profound. Environmental compliance is now split across at least three levels: core IMO prevention and certification duties, IMO carbon-intensity duties, and EU carbon-cost/fuel-intensity duties. A ship can therefore be technically MARPOL-compliant and still face separate EU non-compliance exposure if its reporting, allowance surrender, or FuelEU monitoring and fuel-pathway position are inadequate.
Port State Control, Commercial Risk, and Enforcement
Environmental compliance is ultimately tested in port. IMO’s 2025 PSC Procedures show that missing or invalid environmental certificates, failed treatment systems, missing SEEMP documentation, ballast-water deficiencies, sewage deficiencies, and AFS non-compliance are all part of real-world inspection practice. In other words, environmental law is not enforced only through large fines after dramatic spills. It is often enforced through documentation review, onboard inspection, and commercial interruption.
That reality changes the legal duty of shipowners and operators. Compliance must be designed to survive inspection, not just internal audit. The ship’s plans, record books, certificates, fuel-management practice, ballast-water procedures, garbage handling, anti-fouling status, and hazardous-material inventory need to be coherent enough that the master, crew, superintendent, and company can prove compliance under scrutiny.
Conclusion
Maritime Environmental Compliance: Legal Duties of Shipowners and Operators is now a full-spectrum legal subject. The global framework begins with MARPOL and its six annexes, extends through the BWM Convention, AFS Convention, and Hong Kong Convention, and increasingly overlaps with the IMO’s carbon-intensity regime and regional systems such as the EU ETS and FuelEU Maritime. The legal duties are no longer limited to “do not pollute.” They include certification, ship-specific plans, record books, surveys, compliant fuels, approved treatment systems, energy-efficiency management, corrective action planning, and lifecycle environmental preparation.
For shipowners and operators, the central legal lesson is clear: environmental compliance in shipping is now a trading condition, a financing issue, an inspection issue, and a liability issue at the same time. The companies that handle it well are not the ones that wait for a port-state deficiency or a pollution incident. They are the ones that treat environmental compliance as a continuous management obligation embedded in ship operations, technical planning, documentation, and contract strategy.
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