Summer water transparency (Secchi depth) observations in the open waters of the Gulf of Riga are available from 1963, in transitional waters from 1983, in coastal waters of the Gulf of Riga from 1991 and in coastal waters of the Baltic Sea from 1999.
Data on bottom oxygen concentrations in the western coast of the Gulf of Riga are available from 1988 to 2006. The number of observations in the year 2007 (Figure 2), but it should be noted that observations have not been regular
Winter observations of DIN (dissolved inorganic nitrogen) in the open and transitional waters of the Gulf of Riga are intermittently available since1974.
Observations of annual mean Total Nitrogen concentrations in the open waters of the Gulf of Riga are intermittently available from 1990 onwards.
Observational results of dissolved inorganic phosphorus (DIP) concentrations in the open and transitional waters of the Gulf of Riga during the winter season are intermittently available from 1974 onwards.
For the assessment of the environmental status, the results of summer season measurements of chlorophyll a from 1996 onwards are used.
