SEL: Ecological State of Lakes

The SEL is an indicator of the ecological status of lakes based on the assessment of trophic status, which, in relation to chemical status, is used to determine the environmental status in accordance with Legislative Decree 152/1999 now repealed. The determination of the SEL is based on the criteria laid down in Ministerial Decree No 391 of 29 December 2003 (which amended the method defined by Legislative Decree 152/1999) and considers transparency parameters, chlorophyll “a”, total phosphorus and dissolved oxygen. For each parameter, a level is identified (variable from 1 to 5, with a deterioration as the level increases) using the appropriate tables provided for in the method. By comparing the sum of the levels attributed to the individual parameters with the ranges set out in Ministerial Decree 391/2003, the SEL class is obtained, which can take values from 1 (better status, blue) to 5 (worst state, red).