The Forth’s unique tidal patterns hold the sewage in the main body of the estuary and it is brought to the shoreline under certain wind and water condituions.
When the tide turns most of the waste returns to deeper water where it is permanently suspended until the next time conditions are right for it to be swept ashore again.
Scottish Water say that £25m of improvement works are needed to help address the problem but has still to unveil a timetable for when these changes, first recommended in 2018, will be made.
The publicly-owned quango said it was committed to "deliver the right solutions in the most sustainable way" for the Firth of Forth.
The affected areas stretch from Falkirk to Edinburgh on the south coast of the estuary, and from Culross to Aberdour on the north side in Fife.
One Fife resident, who has lived in Culross for more than 30 years, told BBC Scotland: "At first when we'd go and do our beach clean-ups we thought where is all this stuffing coming from because it looked exactly like you'd find inside a sofa.
"It took us a long time to realise what it was, it's so engrained and shredded that it doesn't look like wet wipes when you first look at it.
"It's disappointing to discover that what you think is a clean beach isn't clean at all and has all these sanitary products entangled in the sand and the seaweed. It's a shame the beach can't be safely enjoyed."
An internal Scottish Water report, released under Freedom Of Information laws, suggests there is "a body of sewage related debris held in suspension within the Firth of Forth that is being washed up along the beaches and is being topped up new sewer discharges".
It is thought most of the waste is discarded wet wipes - the biggest contributors to blockages in Scotland's sewer network. They were never intended to be flushed into the sewage system and even many which claim to be bio-degradable take years to break down.
The 2018 report makes a total of 27 recommendations including improving screening of sewage debris and building better waste overflow facilities.
Earlier this year, it emerged that the number of recorded sewage spills in the country's rivers and seas has increased forty per cent over the last five years.
A Scottish Water spokesman said it takes its environmental responsibilities "very seriously" and responded to any issues raised.
He added: "The study set out to understand the potential sources of sewer related debris in the Forth and was commissioned partly in response to local concerns.
"We understand that the time it takes to plan, prioritise and fund solutions can be frustrating, but it is important that we deliver the right solutions in the most sustainable way.
"We are committed to reducing the amount of sewage-related debris in water bodies in and around Scotland through more monitoring, targeted investment and campaigns around unflushable items."