SATURDAY morning parkgoers arrived at East Shores to find the Rotary Waterfall was awash with foam.
Suspected youths emptied two bottles of detergent into the waterfall, which flows from Victoria Park at the Auckland Point lookout to the base of HMAS Gladstone.
The bottles were found in nearby bushland.
The windy conditions on the day swept the thick foam north for metres onto surrounding park space used by parents and children.
Gladstone resident Liza Barba said it was a stupid thing someone has done for fun.
"It's just terrible because someone has to come and clean it up now," she said.
"Normally when we come down here it's beautiful and clean but now, well what an idiotic thing to do.
"Ideally in the future I'd like to see a light put in for night time and some fish, but then this could happen again."
The crime happened the day before Gladstone Ports Corporation officially opened East Shores with a family fun day.
A GPC spokesperson said the act was escalated as a priority, and the GPC would have the area cleaned up in time for the opening.
Just weeks prior, 24 hour CCTV surveillance cameras were installed around the area to provide 'a safe and relaxing place for the community'.
The GPC is investigating.