Principle of Good Neighbourliness in Environmental Law

The Principle of Good Neighbourliness is a fundamental rule of international environmental law that regulates the conduct of States whose activities may affect other countries. It recognises that environmental harm does not remain confined within political borders. 

Accordingly, every State must exercise its sovereign rights responsibly, prevent transboundary environmental damage and cooperate with neighbouring States in protecting shared natural resources and the global environment.

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Meaning of the Principle of Good Neighbourliness

The Principle of Good Neighbourliness requires every State to conduct activities within its territory in a manner that respects the rights and interests of other States. A country may use its land, water, forests, minerals and other natural resources, but such use should not cause serious environmental harm to neighbouring countries or areas beyond national jurisdiction.

The principle is especially important because air, rivers, oceans, wildlife and ecosystems do not follow political boundaries. Smoke released from an industrial plant may travel into another country. Polluted water may flow through an international river. Hazardous substances released near a border may affect the health, agriculture and natural resources of people living in another State.

Good neighbourliness, therefore, places environmental responsibility alongside territorial sovereignty. It does not prohibit economic development or the use of natural resources. Instead, it requires States to balance their development needs with the duty to avoid causing environmental injury to others.

Legal Basis of the Principle

The Principle of Good Neighbourliness is based on the broader idea that States must respect each other’s sovereignty, territorial integrity and legitimate interests. In environmental law, this idea is expressed through the rule that one State must not use its territory in a way that causes significant damage to another State.

The principle is closely connected with the Latin maxim:

“Sic utere tuo ut alienum non laedas.”

The maxim means that a person or State must use its property in such a manner that it does not injure the property or rights of another. In international environmental law, the maxim has developed into the no-harm rule.

Under the no-harm rule, a State is expected to exercise due diligence to prevent activities within its jurisdiction or control from causing significant environmental harm outside its territory. The obligation is not based only on whether damage actually occurs. It also requires reasonable preventive action where the risk of transboundary harm is known or reasonably foreseeable.

Essential Elements of Good Neighbourliness

The Principle of Good Neighbourliness contains several connected environmental obligations.

Duty to Prevent Transboundary Harm

The primary obligation is to prevent significant environmental harm from crossing national boundaries. States must identify dangerous activities, regulate industries, supervise private operators and adopt appropriate environmental standards.

The obligation is generally one of due diligence. A State is expected to take all reasonable measures that a responsible government would take in similar circumstances. Absolute prevention of every possible injury may not always be practical. However, failure to adopt reasonable laws, monitoring systems or safety precautions may amount to a breach of international responsibility.

Duty to Cooperate

Environmental problems involving shared resources cannot be addressed effectively by one country acting alone. States are therefore expected to cooperate through bilateral agreements, regional institutions, scientific programmes and international organisations.

Cooperation may involve joint monitoring of rivers, forests, oceans and air quality. It may also include coordinated emergency responses, common pollution standards and shared conservation programmes.

Duty to Notify

Where a proposed activity may cause significant transboundary harm, the State of origin should notify the potentially affected State. Notification must be given sufficiently early so that the affected country has a meaningful opportunity to study the risk and respond.

The information supplied should ordinarily include the nature of the activity, its location, the expected environmental impact and the proposed preventive measures.

Duty to Consult

Notification should be followed by consultation in good faith. Consultation allows the concerned States to discuss the risks, consider alternatives and agree upon preventive or compensatory measures.

The duty to consult does not necessarily give the affected State an absolute power to prohibit the proposed activity. However, its concerns must be considered seriously and not treated as a mere formality.

Duty to Exchange Information

Good neighbourliness requires States to exchange relevant scientific, technical and environmental information. Such information may concern pollution levels, industrial risks, water quality, proposed dams, nuclear facilities, hazardous substances or ecological changes.

Access to accurate information enables neighbouring States to assess risks and take timely protective action.

Duty to Conduct Environmental Impact Assessment

An environmental impact assessment is necessary where a planned activity may create a risk of significant transboundary environmental damage. The assessment studies the possible effects of the project before approval is granted.

In a transboundary context, the assessment should consider not only domestic environmental effects but also consequences for neighbouring countries. It may examine alternative locations, technologies, safety measures and methods of reducing harm.

Duty to Provide Emergency Assistance

Where an environmental accident occurs, the responsible State should promptly inform affected countries and provide available assistance. This obligation is particularly important in cases involving nuclear accidents, oil spills, chemical leaks, forest fires and industrial disasters.

Timely communication may reduce loss of life, environmental destruction and economic damage.

Relationship Between State Sovereignty and Environmental Responsibility

State sovereignty gives every country the authority to control and use the natural resources found within its territory. This includes the power to regulate industries, agriculture, mining, energy production, infrastructure and other developmental activities.

However, sovereignty is not unlimited. A State cannot rely on its sovereign rights as a justification for causing environmental damage to another country. Modern international environmental law recognises that sovereign rights are accompanied by corresponding responsibilities.

This balance has two important elements:

• Every State has the sovereign right to exploit its natural resources according to its own environmental and developmental policies.
• Every State also has the responsibility to ensure that activities within its jurisdiction or control do not cause environmental damage to other States or to areas beyond national jurisdiction.

The Principle of Good Neighbourliness brings these two elements together. It allows States to pursue development while requiring them to consider the environmental consequences of their actions beyond their borders.

Development of the Principle in International Environmental Law

The Principle of Good Neighbourliness did not emerge from a single treaty or judgment. It gradually developed through international practice, judicial decisions, arbitral awards, declarations and environmental agreements.

Earlier principles of international law focused mainly on territorial sovereignty and non-interference. As industrialisation increased, it became clear that activities carried out within one territory could have serious consequences in another. Transboundary air pollution, water pollution, nuclear accidents and hazardous waste movement demonstrated the need for a more cooperative legal approach.

International environmental law consequently began to recognise that States must not merely avoid deliberate injury. They must also take reasonable measures to prevent accidental, indirect and long-term environmental harm.

The principle now supports several legal duties, including prevention, notification, consultation, environmental impact assessment, information sharing and cooperation.

Trail Smelter Arbitration

The Trail Smelter Arbitration is one of the most important decisions associated with the Principle of Good Neighbourliness and the no-harm rule.

The dispute arose between the United States and Canada. A smelter located in Trail, British Columbia, released sulphur dioxide fumes. The fumes travelled across the international border and caused damage to forests, agricultural land and property in the State of Washington in the United States.

The arbitral tribunal held Canada responsible for the damage caused by the smelter. It declared that no State has the right to use or permit the use of its territory in a manner that causes serious injury through fumes in the territory of another State, where the consequences are established by clear and convincing evidence.

The decision is significant because it established that territorial sovereignty does not permit transboundary environmental harm. It also showed that a State may be held responsible for activities carried out by private industries operating within its territory where the State fails to control those activities.

The Trail Smelter Arbitration remains a foundational authority for the rule that States must prevent significant environmental harm to neighbouring countries.

Corfu Channel Case

The Corfu Channel Case also contributed to the development of the duty of States to prevent harmful activities within their territory.

The dispute concerned explosions caused by mines in Albanian territorial waters, which damaged British warships. Although the case did not directly involve environmental pollution, the International Court of Justice stated that every State has an obligation not to knowingly allow its territory to be used for acts contrary to the rights of other States.

This observation became important in the development of international environmental obligations. It supports the view that a State cannot remain passive when activities within its territory create a known risk to another country.

In environmental matters, this means that States must establish laws, regulatory authorities, monitoring systems and enforcement mechanisms to control activities capable of causing transboundary damage.

Stockholm Declaration, 1972

The Principle of Good Neighbourliness received clear recognition in the Stockholm Declaration on the Human Environment, adopted in 1972.

Principle 21 of the Stockholm Declaration recognises that States have sovereign rights over their natural resources. At the same time, it places a responsibility upon them to ensure that activities within their jurisdiction or control do not cause environmental damage to other States or to areas beyond the limits of national jurisdiction.

This formulation became one of the most influential rules in international environmental law. It reflected the balance between national sovereignty and international environmental responsibility.

Principle 24 of the Stockholm Declaration also stresses international cooperation. It states that environmental matters should be handled in a cooperative spirit by all countries, whether large or small, on an equal basis. Bilateral and multilateral cooperation is considered essential for controlling, preventing, reducing and eliminating adverse environmental effects.

Rio Declaration, 1992

The Rio Declaration on Environment and Development reaffirmed the principle in 1992.

Principle 2 of the Rio Declaration recognises the sovereign right of States to exploit their resources according to their environmental and developmental policies. It also repeats their responsibility to ensure that activities within their jurisdiction or control do not cause environmental damage to other States or areas beyond national jurisdiction.

The Rio Declaration is important because it places the no-harm rule within the broader framework of sustainable development. Development is recognised as necessary, but it must be pursued responsibly and without transferring environmental costs to neighbouring States.

Principle 19 of the Rio Declaration further requires States to provide prior and timely notification and relevant information to potentially affected States regarding activities that may have a significant adverse transboundary environmental effect. It also encourages consultation at an early stage and in good faith.

Application to Shared Natural Resources

Good neighbourliness is particularly relevant where States share natural resources.

International Rivers

Rivers often pass through more than one country. Pollution, excessive extraction, dam construction or diversion in an upstream State may seriously affect downstream States.

Good neighbourliness requires reasonable and equitable use of shared watercourses. It also requires prior consultation where a project may alter water flow, quality or ecosystem health.

Transboundary Air Pollution

Air pollution can travel over long distances. Industrial emissions, smoke, chemicals and other pollutants may cross borders and affect neighbouring populations.

States must therefore control major sources of air pollution and cooperate in monitoring and reducing emissions.

Shared Forests and Wildlife

Forests and wildlife habitats may extend across borders. Deforestation, poaching, fires and destructive development in one State may damage an entire ecosystem.

Joint conservation programmes, information sharing and coordinated enforcement are necessary to protect such resources.

Oceans and Marine Environment

Marine pollution caused by oil spills, industrial discharge, plastic waste and hazardous substances may spread across territorial waters. Coastal States must take preventive action and cooperate in protecting the marine environment.

Good Neighbourliness and Other Environmental Principles

The Principle of Good Neighbourliness is closely related to several other principles of environmental law.

The precautionary principle requires protective action where there is a risk of serious or irreversible harm, even when complete scientific certainty is unavailable. Good neighbourliness strengthens this duty where the possible harm may affect another State.

The prevention principle focuses on stopping environmental damage before it occurs. This is central to good neighbourliness because transboundary damage may be difficult or impossible to reverse.

The polluter pays principle requires the person or entity responsible for pollution to bear the cost of prevention, control and restoration. In transboundary cases, it supports compensation and remediation.

The principle of sustainable development requires economic development to be balanced with environmental protection. Good neighbourliness ensures that one State’s development does not take place at the environmental expense of another.

State Responsibility for Transboundary Environmental Harm

A State may incur international responsibility where it breaches an environmental obligation and causes significant harm to another State.

Responsibility may arise where the State itself carries out the harmful activity. It may also arise where a private company causes the damage and the State fails to regulate, supervise or control the activity with due diligence.

Possible consequences include cessation of the harmful activity, assurances against repetition, restoration of the damaged environment and payment of compensation.

However, establishing responsibility may be difficult. Environmental damage may have multiple causes, may develop slowly and may involve scientific uncertainty. Proving the source of pollution and the connection between an activity and the harm may require detailed technical evidence.

Conclusion

The Principle of Good Neighbourliness is a central foundation of international environmental law. It recognises that territorial sovereignty must be exercised with respect for the environment and rights of other States. 

Through duties of prevention, cooperation, notification, consultation and environmental assessment, it seeks to control transboundary harm before serious damage occurs. Its effective implementation promotes sustainable development, environmental security and peaceful relations among neighbouring countries.