Throughout Vietnam there are the traditional hamlets, turned villages, turned suburbs. Something they all still retain, or a characteristic that has withstood the period of development, is the community lake. Used for fishing, bathing and general dumping - they are quite an asset to the suburb. Obviously as time goes by, and trash grows thigh-high these lakes can be more of a burden than a benefit to its society.
What do we do with them now? They cannot efficiently be dredged because there are so many of them, and they can't just be filled in or paved over because they are used often. A solution that seems to be more and more prevalent these days is the use of suspended plants or constructed wetlands - which act as a filter and absorber of toxins in the water. Using plants in this way, for phytoremediation purposes, is now a practical passive and economical way to clean those bodies of water that don't have other traditional alternatives. Throughout the world, different plants - often reeds - are great at taking up excess nutrients and chemicals and using them for growth (storing everything they cannot use in their tissues). In the future I hope these incredible ecological technologies make their way into city water bodies throughout the world just like they are starting to in Hanoi.
Small plug - John Todd Ecological Design has been a pioneer in making these floating plants structures, or Canal Restorers. They have engineered and mastered the science behind many different plant species, making them highly efficient at removing pollutants. One such project can be seen in the Baima Canal, Fuzhou, China (here).