Through the center of the park, a linear constructed wetland, 1.7 kilometers (one mile) long and 5–30 meters (16.5–100 feet) wide was designed to create a reinvigorated waterfront as a living machine to treat contaminated water from the Huangpu River. Cascades and terraces are used to oxygenate the nutrient rich water, remove and retain nutrients and reduce suspended sediments while creating pleasant water features; Different species of wetland plants were selected and designed to absorb different pollutants from the water. Field testing indicates that 2,400 cubic meters (500,000 gallons) per day of water can be treated from Lower Grade V to Grade III. The treated water can be used safely throughout the Expo for nonpotable uses, and save half a million US dollars in comparison with conventional water treatment.