Fish return to Lake Biwa will be made again this year at the Niihama Biotope on October 22, 2017 from 10:00 to 12:00. This is an annual event held every year since 2009 and since 2012, school children and their parents and guardians have been invited to join this activity to learn the natural life of water cratures of Lake Biwa. They will be taught by Japan Water Agency, who manages the biotope about the current severe environmental situation, which Lake Biwa faces now, i.e. the decline of the number of its native fish species such as carps and crucian carps as well as drastic increase of foreign fish like black basses and blue gills. They will recognize that their actions will become a small but important help to conserver the natural environment as well.

Niihama Biotope is a spawning ground for carps and crucian carps. Native adult fish like carps and crucian carps move to inner lakes and paddy fields adjacent to Lake Biwa in spring and spawn there. Then newly born young fish return to Lake Biwa as they grow. When they become adult fish, they come back to those inner lakes and paddy fields for spawning. This is the regular life cycle of local fish in Lake Biwa. However in recent years, there are increasing nuber of foreign fish species like black basses and blue gills in this lake. In addition, there appears the decline of indigenous fish in the lake mainly due to fewer chances for fish to reach inner lakes or paddy fields because of the disconnection from the lake to them and the decline of appropriate spawing grounds because of the environmental degradation. To respon to such a situation, Lake Biwa Development Integrated Operation and Maintenance Office developed Niihama Biotope in 2007 as one of the spawning grounds for carps and crucian carps.