The Sliding Baseline

Why the river you think is healthy and the garden you think is wild are both haunted by an abundance you never experienced, and what shifting baseline syndrome means for anyone trying to bring nature back

Stand on a bridge over a lowland river on a bright morning. The water runs more or less clear. A moorhen picks along the margin, willows lean over the bank, a couple of mallard drift past. It looks, by any ordinary reckoning, like a healthy river. A nice river. The kind of river you would be pleased to have at the end of your road.

You are looking at a ghost.

Not because the scene is fake, but because the yardstick you are measuring it against was handed to you already broken. What you think a river should be is simply what rivers were like when you first started noticing them, and by the time you started noticing, the river had already lost most of what it once held. The abundance that a person standing on that same bridge two hundred years ago would have taken for granted has gone so completely that you have no memory of it, cannot miss it, and so call its absence health. This quiet, generational forgetting has a name.

The idea, and where it came from

The concept is called shifting baseline syndrome, and it was named almost by accident. In 1995 the fisheries scientist Daniel Pauly was asked by the editor of the journal Trends in Ecology and Evolution to write a one-page filler at short notice, because another contributor had failed to deliver. He dashed off a short essay with no data and no equations, and it went on to become one of the most cited things he ever wrote (Pauly, 1995; Mission Blue, 2013).

His observation was deceptively simple. Each generation of fisheries scientists, he noticed, took the state of fish stocks at the start of their own careers as the normal baseline, and measured decline against that. The next generation, inheriting stocks that had fallen further, took that lower level as their normal, and measured against that. And so on, down and down, with each generation quietly accepting a more depleted sea as the natural order (Pauly, 1995). The losses were real and enormous, but they became invisible, because the reference point slid down in step with the decline. As Pauly liked to tell his students, to document change is not enough, because the baseline adjusts itself to the change so that the change is never perceived.

It is, at heart, a form of collective amnesia, and it turned out to describe far more than fish. The environmental writer George Monbiot has made it one of his central themes, and the psychologist Peter Kahn gave the individual version its own name, environmental generational amnesia, the way each child calibrates their sense of a normal, healthy environment from whatever degraded version happens to surround their own childhood (Kahn, 2002; Oceana, 2015). We do not grieve what we never knew we had. That, more than any single pollutant, is why ecological loss is so strangely easy to live with.

The river, writ large

Rivers are the grand, catchment-scale demonstration of the syndrome, because the gap between what we call healthy and what was actually here is so vast.

Take the eel. Most people under fifty have no strong sense that the European eel was ever anything other than a curiosity, and yet it was once one of the most abundant animals in British fresh water. In some European freshwater habitats eels made up more than half of all the fish by weight, and they were a vital part of the food web, feeding otters, herons and bitterns. Within living memory that abundance has collapsed. The eel population in England has fallen by around 95 per cent in the last forty years, and the number of young eels returning up rivers such as the Thames is now roughly a tenth of what it was before the 1980s. The species has been listed as critically endangered since 2008. A child fishing that river today, seeing no eels, is not seeing a healthy river. They are seeing a baseline that slid so far it took an entire keystone species down with it, unremarked.

The same is true of salmon, the fish that once defined our rivers so completely that historical apprentices are said to have bargained not to be fed it too often. Forty years ago an estimated 1.4 million salmon returned to UK rivers each year. We are now at barely a third of that, a new low. The 2024 assessment found that 90 per cent of principal salmon rivers in England are classed as at risk or probably at risk, and salmon stocks have fallen to their lowest level since records began. Salmon are an indicator species, a barometer of the whole freshwater and marine system, and the barometer is reading close to empty.

Zoom out and the pattern holds worldwide. Populations of migratory freshwater fish have fallen by 76 per cent since 1970, and the largest species, the mega-fish weighing more than thirty kilograms, by 94 per cent. And it is not only the animals. The physical river itself has been quietly reshaped into something a wilder eye would barely recognise: straightened, dredged, dammed with weirs and sluices that block migration, and tidied of the fallen trees and log-jams that a natural river is full of and that we now instinctively clear away as mess. We have even normalised the pollution. On the most recent official assessment, not a single river or lake in England was rated in good overall health, making English waters among the worst in Europe, where the average is around 40 per cent in good condition.

Here is the sobering part. Almost nobody experiences this as a loss, because almost nobody alive remembers the river any other way. Each generation inherited a poorer river and simply called it the river. The Victorian would have seen our celebrated beauty spot as a wreck. A medieval Londoner would find our Thames eerily empty. The baseline has slid, quietly and continuously, all the way down to the ghost we now call healthy.

The garden, writ small

If the river is the syndrome at its grandest, the garden is the syndrome at its most intimate, and in one crucial way it matters even more, because the garden is where most of us actually form our baseline in the first place, as children.

Consider what we have learned to call a nice garden: a clipped lawn, some tidy borders, a fence, a paved sitting area, a few bedding plants bought in flower. That picture feels normal, even correct, the way a garden is supposed to look. But that neatness is itself a shifted baseline, an inherited aesthetic of control that reads to us as order and to almost everything else as desert. We did not choose it against the alternative. We simply absorbed it as children and mistook it for the natural state of a garden.

The clearest everyday proof is the windscreen. Anyone old enough remembers long summer drives that left the glass thick with squashed insects, needing a scrub at every stop. Younger drivers have no such memory, and so do not perceive the clean windscreen as a loss at all. Yet the loss is real and measured. The Bugs Matter survey, which counts insects splatted on number plates, has recorded falls of around 60 per cent in flying insects across Britain in just the few years since 2021, and a long-term study in German nature reserves found flying-insect biomass had dropped by more than three-quarters over twenty-seven years. The insects vanished, and because the youngest witnesses never knew the old abundance, the vanishing left no felt trace.

The same creeping recalibration has happened to the dawn chorus. House sparrows and starlings were once so common in British gardens that nobody thought to count them, and both have since declined so steeply that the RSPB's long-running Big Garden Birdwatch shows today's ordinary garden holding a fraction of the birds it did when the survey began (RSPB Big Garden Birdwatch). A child listening at an open window this spring will hear a chorus, and will grow up believing that thinner chorus is what a full one sounds like. The quiet has become the new normal, one generation at a time.

Why this matters, and what it changes

Put the two scales together and you see that the river and the garden are the same telescope pointed at different distances. Both look fine. Both are judged against a baseline that crept downwards below the reach of living memory. And in both cases the danger is not only the loss itself but what the loss does to our idea of success.

Because if our baseline has shifted, then so have our targets. We set out to restore a river or rewild a garden, and without noticing we aim at a version of health that is already a shadow of the real thing. We celebrate a river reaching good ecological status that a Georgian angler would have pitied. We call a garden with a few more bees a triumph. The recovery we are proud of is measured from the ghost, not from the living original. Breaking the amnesia is therefore not a sentimental exercise. It is the difference between restoring nature and merely slowing its decline while congratulating ourselves.

And this is exactly where the humble garden turns out to be the most powerful lever available to an ordinary person, for two reasons that the grand scale of the river cannot match.

First, the garden is where children set their baseline, which means a richer garden resets the reference point for the next generation upward instead of down. The child who grows up with a pond full of frogs, a lawn loud with grasshoppers, and summer evenings thick with moths will carry that higher baseline into adulthood, and will defend a richer world because they remember one. A wilder garden is, quite literally, a gift to the future's sense of what normal should be.

Second, the garden is the one place where you can feel the baseline move back within your own lifetime. Rewild a corner, dig a pond, leave the grass long, let the fallen wood lie, and the abundance that returns over a few short years will recalibrate you in real time. You watch normal shift upwards. The river seldom lets you feel that. The garden hands it to you.

Where to begin

The practical response to shifting baseline syndrome has two halves, and you can do both from home.

The first is to recover the historical baseline in your own head. Read the old accounts of the river you live beside. Find out what your area held a century ago, what fish ran the water, what birds filled the hedges, how loud the summer once was. Pauly's whole point was that to know what has been lost you must go looking for what was there before, deliberately, because your memory alone will keep lying to you by omission.

The second is to reset your felt baseline by making a patch of ground richer than the one you inherited. A pond is the single most transformative thing you can add, followed closely by simply doing less: leaving grass long, letting seed heads and dead stems stand through winter, tolerating the mess that life actually needs, and putting down the sprays. Then pay attention as the abundance returns, and let it move your sense of normal upwards.

And remember that the garden and the river are not separate projects. Every garden sits in a catchment, and every catchment drains to a river, which is why campaigns like the Rights of the River Ouse here in Sussex frame the whole landscape, gardens included, as part of the river's body. The recalibration you perform on your own few square metres is the same act, at the smallest scale, as the restoration of a whole river, and it feeds directly into it.

We cannot fully rebuild the deep abundance of the past, and not every part of it should be romanticised. But we can refuse the quiet trick the syndrome plays on us, the endless renaming of degraded as normal. The river you think is healthy and the garden you think is wild are both ghosts of themselves. The remarkable thing is that the ghost can be fed. Every pond dug, every strip left long, every old account remembered and passed to a child, nudges that baseline back up. The most radical thing you can do for nature may simply be to remember what was here.

References

Pauly, D. (1995). "Anecdotes and the shifting baseline syndrome of fisheries." Trends in Ecology and Evolution, 10(10), 430. The original one-page essay naming the concept.

Alleway, H. K. et al. (2023). "The shifting baseline syndrome as a connective concept for more informed and just responses to global environmental change." People and Nature (British Ecological Society). A recent review of the concept's history and reach.

Kahn, P. H. (2002). "Children's affiliations with nature: structure, development, and the problem of environmental generational amnesia," in Children and Nature, MIT Press. The psychological, individual-scale version of the same idea.

Oceana (2015). Daniel Pauly and George Monbiot in conversation about shifting baselines syndrome. On how the concept spread beyond fisheries. Available at: oceana.org.

Wildlife and Countryside Link / Environment Agency (2020). Water Framework Directive classification for England (no river or lake in England in good overall health; European context). Available at: wcl.org.uk.

Zoological Society of London / Thames Rivers Trust. The European Eel briefing (roughly 95 per cent decline in England over 40 years; recruitment at about 10 per cent of pre-1980s levels; critically endangered since 2008). Available at: thamesriverstrust.org.uk.

Rewilding Britain. European eel species page (once more than 50 per cent of fish biomass in some freshwater habitats; role in the food web). Available at: rewildingbritain.org.uk.

Environment Agency and Cefas (2024). Atlantic Salmon Stock Assessment / "Salmon stocks in England lowest on record" (90 per cent of principal English salmon rivers at risk or probably at risk; roughly 1.4 million UK salmon forty years ago, now around a third). Available at: gov.uk.

WWF / World Fish Migration Foundation (2020). The Living Planet Index for migratory freshwater fish (76 per cent global decline since 1970; mega-fish down 94 per cent). Reported at: wwf.org.uk.

Hallmann, C. A. et al. (2017). "More than 75 percent decline over 27 years in total flying insect biomass in protected areas." PLOS ONE, 12(10).

Buglife and Kent Wildlife Trust. Bugs Matter survey (around 60 per cent decline in insect number-plate splats across Britain, 2021 to 2025). Available at: buglife.org.uk.

RSPB. Big Garden Birdwatch long-term trends (steep declines in once-ubiquitous garden birds including house sparrow and starling). Available at: rspb.org.uk.