In the 1860s, the Water of Leith at Leith was officially the foulest waterway in Scotland. This was unsurprising. Corstorphine and Balerno upstream used it as an open sewer, and for the plentiful mill tanneries it was a free means of waste disposal for the fat they were scraping off the animal hides.

It was tidal at the time. At high tide sea-going ships passed through the central span of Sandport bridge – you can see that the newer stonework replaces the bascule-raised sections.

At low tide the upstream filth was exposed on the muddy banks, with the river trickling along the bottom. It was a serious public health issue.

In 1969 the Duke of Edinburgh pressed a button at the outer lock, in the pagoda building. Ever since, the whole of the dock area and the rivermouth to the top of the tidal reach at West Bowling Green Street bridge is permanently held at approximately 1 foot higher than mean high tide.

It was a very significant intervention into natural forces.

The solids that are carried in any river are deposited where it loses speed. One entirely foreseeable consequence is that, while the docks are dredged for shipping, the riverbed – the responsibility of Forth Ports – along the whole length of the tidal reach is steadily rising.

What you see now – those unsightly islands of large timbers and other rubbish at Shore – is the inevitable result. If it goes on like this for another half-century, it will be a slow-moving quagmire.

Much of the Water of Leith’s lower catchment area is ‘impermeable’ – that is, it is urbanised, and rainfall is gullied directly into the river, a much quicker process than natural drainage.

Upstream, numerous natural flood plains, large and small, have been obliterated. For example, the loop in the river at Bonnington Mill was a good place for a water mill, and problematic for a housing scheme. It was flooded in 2000, with a great deal of damage done, an expensive night for the insurance companies.

On this occasion, exceptionally, the outer lock was fully opened to equalise with sea level. That’s not possible at anything but a high tide. Because of shipping in the docks, Forth Ports must maintain water levels within a very small range.

Thanks to Edinburgh council, the Bonnington Mill scheme is now safe behind flood prevention walls. But all flood prevention measures heighten the potential for problems downstream.

It’s not a question of if there will be a major flood. It’s a question of when. The shallow water and the near-certainty of debris backing up against the piers and arches of the bridges will combine to make it impossible to mitigate on the day.

Leith Shore is at the heart of a man-made mismatch: accelerated delivery and a hold-up at the point of discharge.

Another direct consequence of the button pressed by the Duke of Edinburgh’s finger in 1969 is the nature of the silt building up below water level. It contains significant volumes of methane. About 20 years ago a very large bubble emerged and exploded, breaking windows above The Ship on the Shore restaurant.

Something like this is likely to happen again and, as methane is highly flammable, it’s not inconceivable that the myriad small bubbles coming to the surface on a hot day could be sparked alight.

For twenty years up to 2020, raw sewage from the Sheriff Brae apartments was piped into the river. The problem was fixed after Friends of Water of Leith Basins (FoWLB) referred the matter. But how were the developer’s drainage plans ever approved?

According to FoWLB, sewers at Keddie Gardens and Coalhill continue to overflow unauthorised amounts of raw sewage into the water.

All this rules out any use of the water for recreation. It’s lovely when people sit out in the sunshine, with their feet over the side wall. Someone will fall in, sooner or later, and then the health issues will be focussed. Why should we wait for that? We know the problems.

For years now invasive buddleia and other hardwoods have taken hold at the water’s edge. It’s not only a poor look – more importantly it is very destructive and will, eventually, bring down the masonry.

Forth Ports, responsible for impounding the riverflow and the upstream effects, has a habit of shrugging off its responsibilities for maintenance of the quayside walls.

This is our public space. It is at the heart of the new Low Traffic Neighbourhood. Sandport Bridge is pedestrianised, with nice riverside pedestrian access. Why are we letting it deteriorate to the point of it becoming hazardous?

The email boxes of our councillors and MSPs should be full of demands to be told what the plans are for protecting and enhancing Leith Shore. Three distinct dangers: flooding, health and safety, and damage to the infrastructure, will not go away if the inaction continues.

Are we heading back to the 1860s?

For 20 years up to 2020, raw sewage from the Sheriff Brae apartments was piped into the river, it still is at Keddie Gardens and Coal Hill. ■