Right until the middle of the twentieth century, accounts of the Norfolk Broads made frequent mention of two things. The first was the gin-clear water, which allowed sailors to see deep into the wetland world beneath. The second was the growth of water plants — including many rare species — which was so profuse that they had to be cut and raked to create channels for navigation.

In the great majority of the 63 Broads, neither of these phenomena remotely pertains today. Almost everywhere the water is green and the once-abundant water plants, deprived of light, have gone. So what has changed in the Norfolk Broads — in just a few decades — to damage their water and wetland life so radically?

On many fronts, the late twentieth century was a time of catastrophic decline for wildlife and wild habitat in the UK. Nowhere is this more true than in our wetlands and rivers which, deliberately and collaterally, were used to carry away effluent from our sewers, farms and industry. In the Broads, a combination of agricultural run-off and poorly-managed sewage led to hugely increased available nutrients in the water. This enabled floating algae to bloom, turning the water green and starving the Broads' rare pondweeds, stoneworts and water milfoils of the light they needed to survive. All of the invertebrate biodiversity associated with them massively declined in consequence. Since the 1970s this has been the status quo over most of the region.

Today, however, we stand at a tipping point for wetland wildlife in the Norfolk Broads and for once the news is good. Since the Broads turned green and their famous water plants dwindled almost to nothing, great progress has been made by agriculture and industry to control harmful run-off. Water in the Broads rivers is no longer burdened by so many nutrients. Just as excitingly, scientists now much better understand the chemical and biological processes which caused and have maintained the dramatic change in water quality in the Broads.

The problem of water quality does not have a single, one-off cause. Once water holds artificially high levels of phosphates and nitrates, and algae have bloomed, nutrients are stored in the silt at the bottom of a wetland. Some fish, such as bream and roach, then have two exacerbating effects. As they feed, they stir up sediment from the bottom of the Broad, making nutrients available in the water to algae once more. They also voraciously predate Daphnia, known commonly as water fleas, which are crucial grazers of floating algae in the water column. So — put simply — in wetlands which historically have held high concentrations of phosphates and nitrates, certain fish can keep water green and thus keep rare water plants rare.

Armed with this knowledge, scientists and conservationists can now shift water quality back to former states, with a technique known as biomanipulation. Norfolk Wildlife Trust, with partners including the Broads Authority, Natural England, the Environment Agency and ECON, has received a grant from the Biffa Awards Partnership Scheme, and further support from Essex & Suffolk Water and Love the Broads, for an ambitious project in the Bure and Ant Valleys entitled Tipping the Balance. Following lessons learned from past biomanipulation projects at Cockshoot Broad and Barton Broad, Tipping the Balance will replace existing infrastructure and build on successes at Barton and install new infrastructure to restore water quality at Ranworth Broad.

To achieve this, some 1,800m of fish barriers will be installed in the two Broads, creating three biomanipulation zones at Ranworth and reinstating a further three at Barton. Fish species involved in maintaining poor water quality will be removed from these zones and released elsewhere. This will prevent fish from churning nutrients and from devouring water-filtering Daphnia over large areas of water (10.7ha at Ranworth and 4.2ha at Barton). This in turn will restore lost water quality, allowing rare water plants such as holly-leaved naiad to flourish, and promoting the recovery of around 800 metres of emergent plants, and habitat for water voles, at the edge of Ranworth Broad. Water quality, plant regeneration and fish movements will be monitored both inside and outside these fish barriers, to assess their impact across the Broads and their associated dykes.

Biodiversity benefits will stretch far beyond clear water and abundant water plants. Clear water will attract larger flocks of winter waterfowl, such as were common in the Broads in Victorian times, and will provide better fishing grounds for common tern, pike, otter and — increasingly a common visitor in summer — osprey. To help the terns further, eight new otter-proof nesting rafts will be installed on the Broads, providing much-needed nest sites for a bird which is declining along the coast, in addition to boosting predation of harmful fish species.

And this is just the start. With phosphate concentrations at a 50-year low in Broads water, and nearby Hoveton Great Broad being restored under a separate biomanipulation project, we believe that Tipping the Balance will live up to its name, freeing enough open water in the Bure and Ant Valleys from the scourge of high nutrients and fish disturbance for the entire area to become clear, healthy water once more. Perhaps within a few years visitors to the Broads can again enjoy the gin-clear water and lush beds of rare water plants for which they were famed in Victorian times. We are hopeful that, with Tipping the Balance underway, they will.