A convenient screening method for tracing the amount of anionic surfactants (AS) in environmental water was developed by applying flow injection analysis (FIA) technique, a simple technique for the automation of wet chemical analyses, to the new solvent extraction spectrophotometry of AS (Motomizu, S., et al., Anal. Chem., 54, 392 (1982)). AS in more than 140 points of river and creek waters were determined by employing the screening method to assess the AS pollution of Saga city. The AS pollution was devided into four stages: scarecely or slightly polluted water; 0-0.1ppm (as sodium dodecyl sulphate), polluted water; 0.1-0.5ppm, highly polluted water; 0.5-1.0ppm, and extremely polluted water; 1.0ppm<. About 70% of all samples contained more than 0.1ppm of AS. The main contaminator was assumed to be the AS in waste water from houses. The AS concentration in all streams in the city tended to increase from upstream to downstream. The dynamics of AS were also investigated by monitoring the fluctuation of AS concentration for 24 hours and for 10 days.