Savijoki is a river in Lieto, Southwest Finland. It is about 28 km long, and its river basin covers an area of 130,5 km².
A part of river Savijoki and its river basin act as the pilot area for project SAVE. The area consists in large part of clay soil fields which are suitable for the gypsum treatment procedure. On the other hand, there are no lakes, which could suffer from the sulfate in gypsum, or acid sulfate soils from which the experience of gypsum treatment is non-existent.
From the upper course of Savijoki a significant amount of data about water quality and volume exists from a long period of time. This data enabled to set up a control area upstream where gypsum is not used. By monitoring the water quality in both areas the effects of gypsum treatment are more easily observed.