Freedom of Passage Under Montreux: How Merchant Ships Transit the Istanbul and Çanakkale Straits

Why It Matters

Under the 1936 Montreux Convention, merchant ships of any flag can transit the Istanbul Strait (Bosphorus) and the Çanakkale Strait (Dardanelles) freely in peacetime, and this is the legal basis of Black Sea trade with the Mediterranean and the world. In practice, that freedom operates inside a dense system of traffic reporting, routeing and safety rules run by Türkiye, because the Straits are among the busiest and most hazardous shipping lanes anywhere.

This guide covers the commercial side of the regime: what Montreux promises merchant vessels, how transit works in practice, and why safety and environmental risk are recurring points of debate. Warship rules and Article 19 are covered by sister publications such as Bloc Politics and The Political Anatomy.

Background

The legal basis: Montreux, Articles 2 to 6

The Convention Regarding the Regime of the Straits was signed at Montreux on 1936-07-20 and entered into force on 1936-11-09. It replaced the straits regime of the 1923 Lausanne settlement and restored Turkish control over the Straits, including the right to remilitarise them.

For merchant shipping, the central provisions are:

• Article 2 (peacetime): Merchant vessels enjoy complete freedom of transit and navigation, by day and night, whatever their flag or cargo, without formalities, subject to the sanitary provisions of Article 3. Pilotage and towage remain optional. Charges are limited to those set out in Annex I and relate to specific services.
• Article 3: Vessels are subject to sanitary control by Turkish authorities, designed so that ships with a clean bill of health can pass without unnecessary delay.
• Article 4 (Türkiye not at war): Merchant vessels keep freedom of transit even if other states are at war.
• Articles 5 and 6 (Türkiye at war or threatened by imminent danger of war): Türkiye may restrict passage, for example by requiring day transit along routes it indicates, and ships of states at war with Türkiye lose the freedom of passage.

The Convention applies to the Çanakkale Strait, the Sea of Marmara and the Istanbul Strait as a single system. The text is short, and it was drafted for a very different maritime world.

Why it still governs the Straits

The 1982 UN Convention on the Law of the Sea (UNCLOS) created a general regime of transit passage for international straits. Article 35(c), however, leaves in place long-standing international conventions that specifically regulate particular straits. Türkiye is not a party to UNCLOS, and Montreux remains the governing instrument. The Straits are also a place where general rules from the International Maritime Organization (IMO), such as SOLAS and the collision regulations (COLREGs), apply alongside the Convention.

From 4,500 ships to a congested corridor

When Montreux was signed, roughly 4,500 vessels a year used the Straits, mostly small and powered by coal or early diesel. Turkish and industry sources now describe annual traffic in the tens of thousands of vessels per strait, including large tankers, LPG and chemical carriers, bulk carriers carrying grain and ore, container feeders and passenger ferries that cross the Istanbul Strait all day.

Geography compounds the volume:

• The Istanbul Strait is about 30 km (19 mi) long, narrows to roughly 700 m (about 2,300 ft) at its tightest point and has sharp course changes of up to around 80 degrees.
• Strong surface currents flow from the Black Sea to the Marmara, with a counter-current below, and fog or storms can close the lane.
• Istanbul, with a population of more than 15 million, lines both shores, and local ferry traffic cuts across the transit lanes.
• The Çanakkale Strait is longer, at about 60 km (37 mi), and its narrows are also demanding, with the current pressing vessels toward the banks.

Collisions in the Bosphorus in 1979 (the Independenta disaster, with dozens of fatalities) and in 1994 (the Nassia and Shipbroker collision, which killed 29 crew and burned for days) hardened the Turkish view that traffic management was a matter of public safety, not only of navigation.

How the practical system developed

Türkiye issued a Maritime Traffic Regulation for the Straits in 1994 and a revised version in 1998, supported by traffic separation schemes and routeing measures taken through the IMO. A Vessel Traffic Services (VTS) network covering the Istanbul and Çanakkale Straits followed in the early 2000s. The regulations have been amended since, so operators should always consult the current text and notices from the Turkish maritime authorities, and their local agents, before planning a transit. The main elements, in general terms, are:

1. Reporting, not permission. Vessels are expected to submit a sail plan and position reports to the VTS. The aim is traffic coordination and safety, not a licence to pass.
2. Routeing and scheduling. Larger vessels and those carrying hazardous cargo may be subject to one-way scheduling, additional separation or tug measures in the narrowest sectors. Exact size and cargo thresholds are set in the regulation and should be verified in its current version.
3. Pilotage. Under Montreux it is optional. Turkish authorities and licensed Turkish pilots strongly recommend it, particularly for large or hazardous vessels, and operators often take a pilot as a risk and insurance decision.
4. Anchorages and waiting. Ships that cannot be scheduled immediately wait at designated anchorages at the northern and southern approaches, which is where queues form.
5. Sanitary control and fees. Health formalities follow Article 3, and charges apply for services such as lighthouses or pilots used, in line with Annex I.

Key Players & Positions

Shipping states and the industry

Black Sea littoral states (Russia, Ukraine, Romania, Bulgaria, Georgia) and major maritime flag and ownership states, with Greece prominent among shipowning nations, depend on predictable transit. Global shipping associations such as the International Chamber of Shipping, BIMCO and INTERTANKO generally support the freedom-of-passage principle and argue that any measure delaying ships should be justified, proportionate and non-discriminatory.

The main commercial concerns raised by operators and some states over the years are:

• queues and waiting time at anchorages, which add cost and can disrupt supply chains for grain, fuel and containers;
• the argument that mandatory-style requirements, such as pilotage or advance notification, risk exceeding the Convention's 'no formalities' wording;
• uncertainty over documentation. A well-documented episode occurred in late 2022, when a long queue of tankers built up while Turkish authorities checked insurance documentation. Ankara described the checks as a safety measure, and the backlog eased once acceptable documentation arrangements were agreed.

Black Sea energy and grain flows

The Straits carry Caspian and Russian oil from Black Sea terminals, Ukrainian and Romanian grain, and a significant share of regional bulk cargo. Kazakhstan's exports through the CPC terminal and the wider energy picture are discussed in Energy Corridors Through Türkiye. How merchant shipping operated during the Russia–Ukraine war and the grain initiative is covered by The Global Anatomy.

Other views

Some legal commentators argue that Montreux is a freedom-of-navigation treaty and that new regulatory layers should be interpreted narrowly. Others note that the Convention does not explicitly address modern tanker sizes, hazardous cargoes or environmental harm, and that coastal states retain the right and duty to protect their populations. Both lines of argument appear in the academic and shipping-industry literature.

🇹🇷 Official Policy · Primary Sources

Türkiye's Position

Ankara presents its role as that of a custodian of an international regime, not an owner of a toll road.

• Strict and impartial implementation. According to the Turkish Ministry of Foreign Affairs (MFA) materials on the Straits, Türkiye applies Montreux scrupulously and equally to all flags. Its legal basis is the text of the Convention itself (Articles 2 to 6 for merchant ships).
• Safety rules are consistent with freedom of passage. Ankara argues that the Maritime Traffic Regulations of 1994 and 1998, and the VTS system, are non-discriminatory safety measures that regulate how ships pass, not whether they may pass. It points to the IMO's role in routeing measures and to the 1979 and 1994 disasters as the reason for them.
• Changed circumstances, constant treaty. The Turkish position, as stated by the MFA, is that the dramatic increase in traffic, vessel size and hazardous cargoes since 1936 creates real risks to life, property and the environment that the Convention's drafters could not foresee. Türkiye does not seek to revise the Convention but to apply it responsibly.
• Environmental and urban risk is a Turkish national concern. Istanbul's more than 15 million residents live on the Strait, and Turkish officials, including the Presidency and the Ministry of Transport and Infrastructure, regularly describe oil, LNG and chemical shipping as a risk to the city and the Marmara ecosystem. Ankara's maritime spatial planning, registered with IOC-UNESCO on 2025-06-12, reflects the same emphasis on managed sea use.
• Montreux remains the governing regime. Türkiye relies on Montreux, together with UNCLOS Article 35(c), as the basis for the Straits regime. It regards Montreux as having supported stability for nearly nine decades and as the foundation of Black Sea security.

For more on how the Straits fit into Türkiye's wider transport role, see The Crossroads Guide.

Source Comparison

Question	Typical shipping and Western-media framing	Turkish primary-source framing
Is passage free?	Yes, Montreux guarantees it, so delays look like possible violations	Yes. Freedom of transit is the rule and Türkiye applies it impartially
Are reporting rules a 'formality'?	May conflict with the 'no formalities' wording if they hold ships up	Safety coordination through VTS, not a permission requirement
Is pilotage required?	Optional in law, but pressure to use pilots is sometimes questioned	Optional under Montreux, strongly recommended because of the hazards
Why queues?	Seen as regulatory friction, sometimes political	Seen as consequence of volume, weather, fog and safe spacing
Environmental risk	Often secondary to trade continuity	Central, given Istanbul's population and Marmara ecosystem
Legal regime	Sometimes confused with UNCLOS transit passage	Montreux governs, preserved by UNCLOS Article 35(c)

The fairest reading is that both sides accept the principle of freedom of passage but differ on how far safety regulation may go. Primary sources are the Convention text, the Turkish Maritime Traffic Regulations and MFA statements. Readers should check the current regulation rather than rely on summaries, including this one. Recorridor's method is explained in Editorial Principles.

Key Terms & Related Guides

• Freedom of transit: the right to pass through the Straits without stopping or seeking permission, as set out in Article 2.
• Annex I charges: fees limited to services rendered, such as lighthouse, sanitary or pilot services.
• VTS (Vessel Traffic Services): shore-based monitoring and communication systems that coordinate traffic in the Istanbul and Çanakkale Straits.
• Traffic separation scheme (TSS): IMO-recognised lanes that keep opposing traffic apart.
• Transit passage: the UNCLOS regime for international straits, which does not displace Montreux in the Turkish Straits.
• Pilotage: local-expert guidance on board, optional in law but widely used in practice.

Related reading:

• The Crossroads Guide: How Türkiye's Straits, Rail Lines and Ports Connect Europe and Asia
• Sea Lanes and Seabed Lines: How Jurisdiction Claims Shape the Eastern Mediterranean's Routes
• What Is the Middle Corridor, and What Role Does Türkiye Play in the Trans-Caspian Route?
• Soft Power Daily on Montreux and Black Sea security

Recorridor presents global and regional affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Position' reflect official Turkish policy and legal doctrines as stated by Turkish primary sources. This article was prepared by the Recorridor Editorial Team.