An investigation has confirmed one of New South Wales' most popular beaches is flooded with "very dangerous" levels of human faeces every time it rains.

Key points: Researchers have found that after heavy rain events, the bacteria level of human faeces in the water at Terrigal beach is dramatically high

Researchers have found that after heavy rain events, the bacteria level of human faeces in the water at Terrigal beach is dramatically high This is dangerous as it can cause a range of illnesses and health issues

This is dangerous as it can cause a range of illnesses and health issues Council is urgently investigating old pipes in the network, as well as local properties, under the suspicion it may be caused by illegal household connections

Although the State Government is investigating the pollution as an issue of "grave concern", Terrigal Beach will not be fixed before summer.

This year, the Central Coast Council has been forced to repeatedly close Terrigal Beach, the Haven and the Lagoon after rain events, due to a surge of bacteria in the water, detected as part of the Terrigal Catchment Audit.

Now, researchers from the University of Technology Sydney (UTS), have determined human faeces are infiltrating the water through old drainage infrastructure and illegal sewerage connections.

Terrigal Beach is closed after rain due to dangerously high bacteria levels, which a study has found it caused by human faeces being flushed into the ocean. ( ABC Central Coast: Emma Simkin )

Data collected in June found that during wet conditions the sewage signature in the stormwater discharge grew by over 100 times — rising to a level that poses a very high risk to human health.

"After heavy rain events the bacteria level of human faeces is dramatically high in the Terrigal waterway, especially around the beach itself and the main pipe coming out coming out at the southern end of the beach," local State member, Adam Crouch said.

"It can put health at risk."

The presence of enterococci bacteria in the water can cause a range of illnesses, including gastroenteritis, flu-like illnesses, dermatisis, nose and throat infections and Urinary Tract Infections.

'Best possible outcome'

"The next step is to determine the source, because it's mainly human and many times higher than the safe limit," Mr Crouch said.

"Trying to track that down is a huge job, as you can imagine, testing single house's sewer and water pipes."

Mr Crouch said he had spoken to the local council and he said the NSW Government stood ready to work "hand in glove with them to make sure we deliver the best possible outcome as quickly as possible".

"There are a lot of older homes in Terrigal that were built many many years ago and there may be sewer systems that weren't hooked up correctly in the first place," he said.

"Maybe they were hooked up into the stormwater system rather than the sewer system and that could be where this effluent is coming from."

The Central Coast Council and Department of Planning, Industry and Environment are now working on determining the location of the illegal sewerage connection.

Locals have been disgusted by the extremely poor water quality and say fixing the problem needs to be a priority over other local projects.

"This is a critical issue and needs to be fixed," Terrigal local, Adam Plummer, said.

"Terrigal Beach is a jewel in the crown and populated by thousands of locals and visitors.

"This is a risk to everyone's health if not fixed"

The ageing sewer system and a number of illegal connections are thought to be the source of human faeces running into Terrigal Beach. ( Supplied: Anthony Horwood )

Development a factor

Residents are concerned about the impacts on health, tourism and local businesses.

"If there is a public health safety risk entering our Beach, how is Terrigal going to keep attracting locals and visitors," Tina Rodley said.

Some residents are critical of the Government and council's focus on development.

"Rampant development in the main part of Terrigal is probably a contributing factor," local resident, Nicholas Turner, said.

"Terrigal beach has had the highest pollution count and lowest water quality on the Coast for around a decade.

"The Government should sort the water quality out before focusing on other developments, like the Terrigal beach walkway"

Terrigal on the NSW central coast is home to 11,000 people and attracts millions of tourists every year. ( ABC Central Coast: Emma Simkin )

'No short-term problem'

The local council said it is treating the issue as a matter of urgency.

"In the network there are still some clay pipes, there's still some asbestos pipes, so we need to look at them and replace them," Council's Director of Environment and Planning, Scott Cox, said.

"We've identified a number of household illegal connections, we've put a number of houses on notice to correct that as well.

"Certainly it could have a negative impact and that's why we're working urgently to try and rectify the problem.

But the Council's Director of Tourism, Russell Mills, is confident the water woes will not impact on local businesses this summer.

"[Maybe it would] if people read headlines and they're reading snippets of what's on Google, but I think most people now having a lot of tools at their disposal to research their travel plan," he said.

"They would dig a bit deeper and follow the news and follow the updates about it.

"I don't think there's going to be a short-term problem, but more importantly I think the fact that there's an operational plan in place is going to help it in the long term."