[1] Additionally, the government has designated the Isumi River a national-level Natural Monument (天然記念物, tennen kinenbutsu).

[2] The source of the Isumi River is in the Kamiueno District of Katsuura City.

Fish in the river include the endangered Tokyo bitterling, ayu, medaka, freshwater eel, Japanese dace, and other species of carp.

Chiba Prefecture is carrying out some work on improving the environment of the Isumi River in Ōtaki area.

[1] The middle and lower parts of the river provide extensive irrigation to paddy fields, which have historically made the area rich in rice production.