Landscape to behold at Formoa.

From this village of Mértola council you can see River Guadiana, as you look at east. It flows northeast but, downstream after the bend, it flows southeast. The village after the bend is Pomarão, where a bridge over River Chança allows traffic to Spain (Huelva Province, Andalousia). The white thin line is that bridge, on the mouth of River Chança on River Guadiana. It's where Guadiana becomes the border until its mouth in the Atlantic, succeeding its tributary Chança in that role.
Large view recommended-