A classical system for expressing pollution with mainly organic matter from point sources is the saprobiological index. This system is also used in the country. Irregular sampling and determination is done by the University of Skopje, Faculty of Biology. Even if it is an older presentation, Map 7.6 shows clearly the high sewage pollution with dominant water quality classes III (alpha-mesosaprob) and IV (polysaprob), especially below bigger cities such as Skopje, Veles, Bitola and Stip, as well as the Vardar River, the Cma River, and the Bregalnica River.