ISSUE:
Whether the Trail Smelter's emissions caused transboundary environmental damage to the United States and violated principles of international law?
Whether Canada, as the state of jurisdiction over the Trail Smelter, is liable for the harm caused and obligated to provide compensation?
Whether measures should be implemented to prevent future harm from the Trail Smelter’s operations?
RULE:
No-Harm Principle: States must ensure that activities within their jurisdiction do not cause environmental harm to the territory of another state, reflecting customary international law.
Responsibility for Preventive Action and Compensation: States are obligated to take preventive measures against transboundary harm and provide adequate compensation for damages caused by activities within their control.