There is a natural stream ecological park named "Yang-Jae Stream" which only takes about 5 minutes from my house. This Yang-Jae Stream was originally a tributary of Han River, one of the major rivers in Korea. However, due to land relocation, urbanization and following influx of population in 1970s, the Stream became so polluted and severely contaminated, and the water grade turned into 5 level polluted water where no animals and plants could live there. In 1995, City of Seoul started a restoring project on the Yang-Jae Stream where the natural river engineering method has been applied in order to make a natural ecological stream.  Much efforts for 5 years from 1995 to 2000 were made such as the removal of the concrete bank protection on both sides, construction of nature-friendly bank protectors, installation of water purification facilities and creation of the riverside wetland, a habitat for migratory birds, and a natural ecology learning site. Now the Yang-Jae Stream is a 15.6 km long that is being taken care of by 3 districts of City of Seoul, where many people enjoy visiting the stream with their families all day, and even late at night.  There are many facilities such as walking and bike roads, swimming pools, water playgrounds, stepping stones, outdoor stages for weekend concerts, small water falls, many kinds of flower gardens and a small rice farm. You can see many animals such as frogs, toads, turtles, lizards , wild raccoons and chipmunks. You can also see many birds such as  the heron, spot-billed duck, jay and kestrel, and many fresh-water fish.  I love riding my bike with my friends from time to time and sometimes I take a walk with my family after dinner. I am so grateful to many people who made efforts to revive the polluted small stream into a natural ecological park as a family fun place.  

Reference: http://www.seocho.go.kr/site/yj/index.jsp