In our jargon in biology, wetlands are nature's kidneys, just as forests are nature's lungs. Water flows inside plants, and it is the plants that work for us, 24 hours a day, 365 days a year. Plants capture all kinds of pollutants and even some oils.
All major urban centres today have wastewater treatment plants. I do not want to advertise for it, but the Auberge Le Baluchon, a very large inn in Saint-Paulin, has spent millions of dollars to create wetlands in order to treat its wastewater. That is an example, a model to follow.
In Montreal's Parc Jean-Drapeau, a large beach has been created on an island and water is filtered there by watershed plants.
We could easily cite similar examples in the United States and Europe. This is a new trend that is much less expensive.