Abstract
The assessment of the trophic state of marine coastal waters is one of the leading initiatives declared in the European Water Framework Directive (WFD). The Baltic Sea is a semi-enclosed ecosystem which consists of subregions with wide salinity and seasonality gradients. Anthropogenic impact results in eutrophication processes on different scales. Efficient eutrophication control and environmental management in the Baltic Sea, according to WFD, requires a prerequisite of common and sensitive indicators for the European coastal waters including the Baltic Sea. In this article the Trophic Status Index TRIX, recently succcesfully implemented in Mediterranean and Northern European sea coastal waters as a holistic approach indicator, was implemented for the Gulf of Rīga and Latvian Baltic Sea coastal water quality assessment between 1999 and 2005.