Water transparency in June-September measured as Secchi depth (m) between years 1903 and 2007 in the Western Baltic Proper

Secchi depth observations (m) are plotted against the year of observation and the curves fitted with non-linear smoothing and shown with 95 % confidence intervals. The preliminary estimation of reference conditions is shown as a red line and the target value with a blue line. The number of observations (n) is shown on each figure.