Highways can gather a lot of pollutants from traffic and air, which can harm water quality when it rains. Scientists studied how wetlands can help clean up this polluted water. They looked at runoff from highways in Ohio and found that wetlands can reduce metals like zinc, iron, lead, and nickel in the water. The wetlands were able to remove 30-90% of these metals, even during winter. The wetlands also helped neutralize the alkaline runoff, making the water cleaner for the environment.