Waterways are any navigable bodies of water used for transportation, trade, or passage. They include natural rivers, canalized rivers, and entirely artificial canals. Together, these routes carry over 80% of global trade by volume, making them the backbone of international commerce. But waterways also serve critical ecological roles, from filtering pollutants to connecting wildlife habitats across fragmented landscapes.
Three Main Types of Waterways
Waterways fall into three distinct categories based on how much human engineering is involved: natural rivers, canalized rivers, and artificial canals.
Natural rivers are the simplest form. Water flows through a drainage basin from rainfall toward a sea or lake, and if the river is deep and wide enough, ships can travel along it. The Mississippi, the Amazon, and the Danube are all examples of natural waterways that have supported trade for centuries. Their depth, speed, and navigability change with the seasons, which can limit when and how they’re used.
Canalized rivers are natural rivers that have been engineered to make navigation easier. The key modification is the construction of locks, which are essentially water-filled chambers that raise or lower boats between stretches of river at different elevations. Think of them as staircase steps for ships. The number and size of these locks depend on the natural slope of the river valley. Modern canalized rivers like the Rhône and the Rhine also incorporate hydroelectric dams, creating deeper locks with longer artificial approach channels that need reinforced banks to prevent erosion.
Artificial canals are entirely human-made channels that can cut through hills, cross watersheds, and pass over valleys. Because they don’t follow a natural water path, their banks and beds often require protection against both erosion and water seeping into the surrounding ground. The Suez Canal and the Panama Canal are the most famous examples, but thousands of smaller canals exist worldwide for regional shipping and irrigation.
How Waterways Are Kept Open
Natural waterways don’t stay navigable on their own. Rivers deposit sediment, water levels fluctuate, and channels shift over time. Maintaining a usable waterway requires constant work. In the United States alone, the Army Corps of Engineers maintains 12,000 miles of inland and intracoastal waterways, along with over 230 lock chambers at nearly 200 sites. On top of that, the Corps manages more than 1,000 coastal and inland harbor channels spanning another 13,000 miles.
The main tools for keeping waterways functional are dredging (removing sediment from the bottom to maintain depth), locks and dams (controlling water levels so ships can pass through areas with elevation changes), and weirs and sluices (structures that manage the flow of excess water around locks). Without regular dredging, many of the world’s busiest shipping channels would become too shallow for large cargo vessels within a few years.
Why Waterways Matter for Global Trade
Ships carry about 80% of all goods traded globally, moving products from production to consumption across oceans and through inland channels. That makes waterways the single most important infrastructure for international commerce.
A few specific waterways carry outsized importance. The Suez Canal, a 193-kilometer channel opened in 1869, sees roughly 50 ships pass through daily, carrying between $3 billion and $9 billion worth of cargo. In 2019, over one billion tonnes of cargo moved through the Suez Canal, four times the volume that passed through the Panama Canal that same year. In 2020, approximately 19,000 ships used the Suez route. Egypt expanded the canal in 2015 by adding a 35-kilometer parallel channel to reduce transit times and increase capacity.
Disruptions to major waterways ripple through the global economy quickly. When a single container ship blocked the Suez Canal in 2021, it held up an estimated $9.6 billion in trade per day. Inland waterways carry a smaller share of total trade but are critical for moving bulk commodities like grain, coal, and construction materials cheaply over long distances.
Ecological Functions of Waterways
Beyond transportation, waterways and the land immediately bordering them (known as riparian zones) provide a range of ecosystem services that are easy to overlook. Riparian zones act as natural water quality buffers. They filter sediment, retain pollutants, and control erosion before contaminants reach the water. In agricultural areas, these buffer zones are especially important for limiting runoff of pesticides, nitrogen, phosphorus, and fine sediments into water sources.
Waterways also function as ecological corridors. In heavily modified landscapes where forests have been cleared for farming or development, the strips of vegetation along rivers and streams often represent the last remaining connections between isolated patches of habitat. Species that depend on tree cover use these corridors to move between populations, which is essential for genetic diversity and long-term survival. Waterways also help regulate flood risk by absorbing and slowly releasing excess water during heavy rains, reducing the severity of downstream flooding.
Legal Classifications of Waterways
Not all waterways carry the same legal status. International maritime law, primarily through the United Nations Convention on the Law of the Sea, divides water into several zones with different rules about who controls them.
Internal waters include all water that falls landward of a country’s coastal baseline: lakes, rivers, and tidal waters. A country has the same sovereign authority over its internal waters as it does over its land territory. Foreign ships have no automatic right to pass through them.
Territorial seas extend up to 12 nautical miles from the baseline. Coastal countries have sovereignty over this zone, including the surface, water column, seabed, subsoil, and airspace above. The key difference from internal waters is that foreign vessels do have the right of “innocent passage,” meaning they can transit through territorial seas as long as they do so peacefully and without stopping.
Beyond a country’s exclusive economic zone, the open ocean is classified as the high seas, which no nation controls. The seabed beneath international waters is considered “the common heritage of all mankind” under international law, meaning no single country can claim it.
These legal distinctions have real consequences. Control over a waterway determines who can charge transit fees, who regulates shipping traffic, and who is responsible for environmental protection. Disputes over waterway sovereignty have triggered international conflicts for centuries and remain a source of geopolitical tension today.