Scientists say western Sydney residents are at risk of swimming in contaminated water.

The New South Wales Government's Beachwatch service tests Sydney's eastern beaches and harbour locations, but not the swimming spots west of Cabarita.

Ian Wright, a water pollution expert at Western Sydney University, says it is a massive omission not to have any public data on water quality at Windsor Beach.

“This is the Bondi Beach of western Sydney,” he told reporters.

“This is incredibly popular but I can't give you any guidance on water quality and the risks involved.

“I don't know how swimmable that is.”

Dr Wright said there could be risks to human health due to the microbiology of the river.

“Historically there have been so many water quality issues here,” he said.

“It has high nutrients, it has blue-green algae from time to time, water weeds, and it also has the likely presence of human pathogens, so bacterial contamination is also an issue here.

“It's a huge act of faith to jump into this water.”

Dr Wright said some local councils have water testing data, but are not releasing it.

“Why do we have so little information available? Yet we have so much development about to hit here and every bit of development will have so many more water quality issues associated with it,” he said.

“If the State Government says that Beachwatch is the responsible authority in the east and the harbour, why isn't it also the responsible authority in the west?”

NSW’s Office of Environment and Heritage says it has “no plans” to widen the Beachwatch program “at the moment”.