The water that flows
in the Cheonggyecheon is a Class-2 level of water quality. Class-1 has a high
environmental adaptability for freshwater fish (Moroco oxycephalus, etc.) and
Class-2 is for fish native to the Hangang(River) (minnow, crustacean, catfish, etc.).
Therefore the water of the Cheonggyecheon is safe for recreational use, and
children can play in the water with no worry of contamination from the habitat.
Source: Cheon Gye Cheon