Shinano-Chikuma River system is the third largest in Japan and at , is the longest river in the country. The river system supports a population of around 3 million () but supports significant agriculture and electricity generation. The river has 880 branches which is the second highest in Japan after the Yodo River. The discharge of the river averages , with a mean maximum of to mean minimum of . In addition to this discharge, of water is used for municipal and industrial supply across the basin. The Chikuma River originates in the Japanese Alps at altitudes of above and has a basin in its own right of . The Chikuma continues generally north-northeast joining with the Sai and changing name to the Shinano, after . The Chikuma, therefore, includes around sixty percent of the whole river system's basin and around 58 percent of the river's length. In the upper reaches of the river, where it is known as the Chikuma, only around ten percent of the land is flat, agricultural land and around of it is irrigated. By the time the river flows onto the Echigo Plain, however, much more land is devoted to agriculture and there is huge potential for irrigation, especially due to influence of the Ohkouz Channel and weir. The abundance of water and fertile soils has led to this area being the one of the best rice producing areas in Japan. Rainfall varies considerably in the Shinano basin. In the middle part of the Chikuma River, near its confluence with the Sai River, rainfall is some of the lowest in Japan, generally staying below . The low precipitation is primarily due to its encirclement by the three ranges which make up the Japanese Alps and by the Jōshin'etsu-kōgen National Park. However, the upper reaches of the Chikuma and Sai Rivers and the lower part of the Chikuma River (where it changes name to the Shinano River) receive annually. In the central areas of the Shinano River, especially in the Uono Basin, precipitation increases to around ; this area receives some of the highest winter snow falls in Japan with 40–50% of this precipitation falling as snow. The heavy snow melt is responsible for much of flooding to affect the Echigo, but also allows for the hydroelectricity generation and regular irrigation. Ecology The Shinano basin supports a large range of plant life, including over 1,100 species