Wollongong City Council closed Unanderra's popular public swimming pool on Wednesday after poo was found in the water and the facility damaged overnight.
Lake Illawarra police are investigating after staff discovered Western Suburbs Pool was broken into and the toddlers and main pools soiled about 5.30am.
The pools had to be emptied and cleaned on Wednesday, which has wasted thousands of litres of water.
Police believe a group of young people entered the facility between 7pm on Tuesday and 5am on Wednesday.
They damaged security shutters, went to the staff room where they smashed a glass panel, threw items around the room, opened cupboards and doors and then went to the canteen area.
A television, small fridge and food items were stolen from the kiosk.
Lane ropes were also wrapped around swim flags and found on the roof of a nearby building.
Wollongong Lord Mayor Gordon Bradbery has urged anyone who might have seen suspicious behaviour near the pool to come forward.
"Please, if anyone knows anything about these criminal acts, we ask you to contact Lake Illawarra Police,'' he said.
"We've had to close the pool today due to the level of damage and this is so disappointing.
"We've had to waste thousands of litres of water emptying, cleaning and refilling the pools, not to mention time and money.
"Whoever broke in obviously spent some time in the pool area and I hope someone saw something."
Cr Bradbery said he was "extremely disappointed" to people in the community would damage the recreational facility.
"These assets are owned and paid for by the people of Wollongong," he said.
"I can't accept this as normal and am disgusted and greatly disappointed by this act."
Officers from Lake Illawarra Police District attended and established a crime scene, which will be examined by specialist forensic officers.
Lake Illawarra Police District Acting Inspector Anthony Peterson echoed Cr Bradbery's disappointment.
"To see a public facility that is there for the enjoyment of the community go through such a senseless act of vandalism is disgusting," he said.
"We are appealing for anyone with information to contact police.
"We would love to identify those responsible."
The act is made even worse as the closure of the pool is in school holidays, when many children and families frequent the facility.
"We apologise to anyone who had planned to visit this popular pool today," Cr Bradbery said.
"We will be working as quickly as we can to reopen it.''
The pool is likely to reopen on Thursday.
Police are urging anyone with information, CCTV or dashcam vision to contact Lake Illawarra police on 4232 5599 or Crime Stoppers on 1800 333 000.