The issue has caught the attention of George Citer, the chairman of the Waterfront Action Group, who in recent weeks has heard almost daily reports of erosion "sinkholes".

"Our members have notified us of substantial damage to their seawalls and other structures on the waterfront and they are blaming the RiverCat ferries…specifically the wake caused by the RiverCats," Mr Citer said.

Waterfront lessees of the land owned by Roads and Maritime Services have been given quotes ranging from $50,000 to $300,000 to repair the damage.

Dr William Glamore, a principal research fellow at the UNSW Water Research Laboratory, said it was possible that wash from the RiverCat ferries was causing erosion.

"There are many reasons you get erosion, but the energy from the RiverCats is completely outside the natural energy of that environment. You wouldn't normally get waves of that size and shape, particularly of the wave period," he said. "That is directly related to wave energy...which causes the erosion."

Dr Glamore said the "sinkholes" to which residents were referring is a process known as "slumping".

"While the RiverCats are likely to be a major source of wave energy, the slumping occurs because older walls, predating the RiverCats, obviously weren't designed for this level of wave energy and the rate at which they are failing could be related to the increased wave energy."

There has been a decades-long campaign against the wash caused by the RiverCat ferries, which dozens of waterfront leaseholders from suburbs such as Drummoyne, Abbotsford, Gladesville and Huntleys Point say are responsible for years of seawall erosion along the Parramatta River.

As the fill behind the seawall is being sucked out by pressure waves, it is causing the land behind the seawall to subside.

"I know of someone in Drummoyne who has spent around $160,000 after two 'sinkholes' appeared. They filled one and roughly a year later they had to fill the second with 35 tonnes of concrete," Mr Citer said.

"We have also been told of a commercial marina that has about $200,000 of damage to its jetties."

Tony Hopkins, who has been repairing seawalls for 38 years, said the majority of the jobs done by his company Australian Seawall Specialists were the same.

"It's a maintenance issue a lot of people don't think about doing. It is their responsibility for them to look after their walls. You can't blame the ferries, but the ferries are causing it."

The  impact of the RiverCat ferries on the Parramatta River was examined more than a decade ago. In 1998, The Sun-Herald reported an independent engineering probe had revealed "more than 70km of land fronting the Parramatta River was dangerously eroded…by the ferries' wave motions".

Abbotsford Point Boatshed owner Roger Kyle said he still experiences deterioration to his waterfront boatshed, where waves wash up through his floorboards daily.

"I'm not the kind of guy to whinge about it ... but it gets to you, you know? You're up against city hall."

Since the 1998 investigation, ordered by the Department of Urban Affairs and Planning, there have been two studies into the use of RiverCat ferries on the Parramatta River, in 2010 and 2013, commissioned by eight local governments.

Both reports found RiverCat wash to be "the primary source of erosion" in areas along the  river.

"A key management issue ... is instigating modifications to or replacement of the RiverCat with another vessel that generates less wash to reduce further erosion by its wash," the 2013 Parramatta River Estuary Coastal Zone Management Plan said.

Lawyer Warwick La Hood is representing waterfront owners in their domestic leasing arrangements with RMS, with whom he is working collaboratively on the issue of seawall damage.

"If RMS are aware and have been put on notice that the way they have managed the movement of RiverCats has caused the degradation to the sea wall, they will be exposed to liability in rectifying the damage."

A spokesman for Transport for NSW said the NSW government's $100 million boost for Parramatta River ferry services includes four new vessels, and the minimisation of vessel wash will be considered in future design options.

"It should be noted that ferry wash is only one cause of erosion. Other causes include natural events such as severe storms, flooding, high tides, wind fetch and public access to sensitive foreshore areas," he said

"From around the late 1990s, the speed limit from Silverwater Bridge to Parramatta Weir was reduced to seven knots with vessels directed to move away from the shoreline where possible to minimise environmental impact."

The RMS would arrange to meet with representatives of the Waterfront Action Group to discuss their concerns, he said.