Road repair crews have been called to Tarra Place in Ngunnawal three times in the past six months, while marsh plants have started growing in some water-sodden backyards.

The unexplained water source, which continues to seep to the surface all over the street and surrounding properties, has sparked fears about structural damage to homes and even the forming of sinkholes.

Authorities are yet to determine the cause of the reservoir, but residents have said issues were first detected following heavy rain in mid-2020.

Some residents said they had spent several thousand dollars in rectification works in an attempt to solve water issues on their property. One resident said water had leaked into their living room, while another said the underground water had seeped into their garage.

In some instances, the reservoir has led to bulrushes - commonly found in marshes and swamps - growing in backyards, even when residents haven't planted them.

A geotechnical report has been commissioned by ACT authorities to determine the cause of the water situation, although the results are not yet known.

The underground water has also led to large potholes developing along the road. Water has been seen seeping out of the potholes, even when it has not rained in several days.

The potholes have been patched over by City Services three times in the past six months.

Road workers were seen at the street on Tuesday fixing over the pothole, after the hole was previously patched over just before Christmas.

However, it's understood the road work earlier this week was a temporary fix before the geotechnical report into the underground water issue was finalised.

Smaller potholes, with water seen running out of them, have also been seen near the street.

City Services has received seven complaints since the potholes were first detected on the road.

Tarra Place resident Liam English has lived on the street for four years. He said the water issues had only developed recently.

"It has seeped into the garage at one point," Mr English said. "We had to put in a lot of extra infrastructure, and a lot of money has been put into it and it's been pretty costly.

"There's been no explanation as to why it's happening." He said the issues were particularly bad following periods of heavy rain.

"If there's heavy rain, it just doesn't drain away," he said. "Even if it doesn't rain for several days, the ground is still very wet."

Strata complexes along Tarra Place have had to introduce special levies for residents just to manage the water issues.

Nada Nikolic has lived on Tarra Place for more than two decades. She said the issues to do with the road and the water only surfaced recently, and that she had spent more than $3000 on drainage measures. "It's certainly not like it was before," she said.

"The water just stays in the ground for so long."

While the potholes caused by the underground water have been patched over, residents said it was a quick fix and that it was only a matter of time before the road was torn up again.

A City Services spokesman said an engineer had been hired to investigate the situation and carry out soil testing with lab results expected to come through later this week.

The spokesman said while the cause of the water issues was initially thought to be leaking pipes, that has since been ruled out. "In the interim, more stabilised road-based material is being planned to be used on this area until the investigations are completed," the spokesman said.

Icon Water investigators were called out to the site four times in 2020, but no fault was identified.