The environmental impact of boats is significant and multifaceted, though it varies greatly between small recreational craft and massive commercial vessels. Large ships are responsible for approximately 3% of global greenhouse gas emissions and a substantial portion of nitrogen oxide and sulfur oxide pollution due to the use of "heavy fuel oil," which is much dirtier than standard diesel. Beyond air pollution, maritime transport contributes to water pollution through oil spills, bilge water discharge, and sewage. Invasive species are also a major concern, as ships transport organisms across the globe in their ballast water, disrupting local ecosystems. Sound pollution from engines and propellers interferes with marine life communication, particularly for whales and dolphins. While sea freight is more carbon-efficient per ton of cargo than air freight, the sheer scale of the industry makes it a critical area for environmental regulation. Recreational boats also impact local waterways through engine leaks, toxic anti-fouling hull paints, and shoreline erosion caused by wakes.