Shoalhaven City Council opened Lake Conjola to the sea at 11:30am this morning, Monday, February 10.
Mechanical intervention was used to open the lake.
To minimise the potential danger to operational staff the lake was opened before the next high tide reaches its peak.
Weather conditions are expected to continue to change throughout the day, with the addition of an expected possible thunderstorm later this afternoon, which may impact on opening operations.
Council engineers are onsite conducting a safety assessment, to ensure the lake entrance is opened to minimise the potential impact of expected high tides.
The Bureau of Meteorology (BOM) have predicted a high tide of 1.8 metres around midday on Monday.
Across the weekend council's flood engineers have been monitoring the Lake Conjola site, along with other Shoalhaven sites.
On Sunday night the lake level was around 0.6 m AHD however, with subsequent significant rainfall, by 3:08am the lake had reached its emergency level of 1.31m AHD.
Operational staff will continue to monitor weather and ocean conditions as the operation continues.
Residents in Lake Conjola are requested to stay outside the work area and keep away from the edges of the dug channel and eroding banks following opening as these areas are very unstable and unsafe.
It is expected that the low-lying areas around the lake will be subject to flooding and people should put in place their flood emergency plan.
Further north and the Shoalhaven River at Shoalhaven Heads has also been opened to the sea.
Council reminds residents that anyone needing assistance should contact the SES on 132 500.