Identifying water quality as the most pressing risk - and also the community's top concern - the two councils' mayors vowed to act.

Wollongong Lord Mayor Gordon Bradbery said the lake was of "paramount importance", while Shellharbour Mayor Marianne Saliba said it was their "duty" to preserve the "fragile" ecosystems around the waterbody.

"The planning and actions that we undertake now will determine the health and protection of the lake and surrounding habitat into the future," Cr Saliba said.

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"The unique diversity of life in and around Lake Illawarra is fragile and requires comprehensive planning and vision to keep it healthy. The lake is special place for both locals and visitors to the area and we have a duty to ensure its preservation."

Water pollution, disturbances from development, and impacts from the lake being opened, were identified as the top three threats.

Changes to development plans to ensure construction did not increase pollution, and monitoring the tidal activity and raised water levels caused by the lake being open, and the effects of climate change, are also among the measures set out.

When, or if, the measures would be implemented is not clear. While the plan indicates the installation of new stormwater structures would "commence by Year 4" after the plan is approved, each action is "subject to available funding".

The Coastal Management Program for the lake has been sent to the NSW Government for certification. Delivering it was estimated to cost $72.8 million.

"How we manage and improve the quality of our lake, its surrounds and continue to make it a wonderful attraction is of paramount importance for both councils," Cr Bradbery said.