The number of alien species increases in the clean river! ~ Report on the 15th city river biological survey results ~

Yokohama City has conducted a survey of fish, benthic animals, aquatic plants, and attached algae about once every three years since 1973 for six water systems of the rivers flowing through the city. We evaluate the water quality of the river. This is the 15th survey. Compared to the results of past surveys, the number of confirmed species has increased along with the improvement of river water quality, but on the other hand, the number of exotic species that appear has been increasing year by year.