Idukki is one of the largest arch dams in Asia. Since it was commissioned in 1975, its dam shutters have been opened only twice — the last time was 26 years ago in 1992. On both these occasions, water was released during the northeast monsoon in October-November. This year, however, it is likely to open during the southwest monsoon. On July 20, 2017, the water level was 2,320 ft compared to this year’s 2,403 ft.