It’s just over two years since a toxic spill turned Oak Beck in Harrogate brown and killed off the river’s wildlife, including hundreds of fish.

It was a catastrophic incident that shocked many who witnessed its aftermath.

Keith Wilkinson MBE, who has led conservation efforts in the area for over 40 years, said at the time that the beck would take three years to recover. This week, he and a band of volunteers from Bilton Conservation Group (BCG) were back on the riverbank to find out how well the beck is bouncing back.

Visual analysis – in other words, taking a look – gives a depressing reading: it looks all but dead. Turning over stones on the riverbed just downstream from Spruisty Bridge at Knox, Mr Wilkinson was hoping to find freshwater crustaceans, molluscs, worms and caddis fly larvae, but found no life at all.

He said:

The September 2022 incident seems to have been the result of two spills on the same day. The first consisted of thick metallic sludge and oily scum thought to have come from the old New Park gasometer, which engineers had been dismantling, and the second is believed to have been a sewage discharge below the Hydro.

A healthy river has 21-30 different life forms living on the bottom – the more variety, the better.

But mayflies, worms, snails and especially stone flies are all particularly vulnerable to pollution from hydrocarbons and heavy metals of the kind that appear to have leaked into Oak Beck two years ago.

That was the worst of a series of incidents going back many years. In just the five years preceding it, the Environment Agency revealed in response to a Freedom of Information request from Mr Wilkinson that there had been 42 reported incidents along the beck.

Most of these involved sewage, which poses a risk for human health. For this reason, one of the BCG volunteers, John Branson, also collected samples for his own programme of testing for E. coli, the faecal bacteria that can cause serious stomach upsets. Early results indicate levels four times the permissible maximum.

Despite the apparent wasteland of the riverbed, Mr Wilkinson did spot a good-sized shoal of minnows under the bridge, and the team’s test samples will help determine what other fish may have returned.

For the DNA testing programme, most of whose costs are being covered by a £1,000 grant from the North Yorkshire Council locality budget of Monika Slater, Lib Dem councillor for Bilton Grange and New Park, the team took water samples from three sites – Oak Beck’s confluence with Cow Dyke Beck, the ford at Knox, and from below the viaduct downstream of Oak Beck’s confluence with the River Nidd.

These will be sent for analysis by a company called Nature Metrics in Surrey, which can distinguish between 14 different UK freshwater fish species.

Mr Wilkinson, who is chairman of Nidd Gorge Advisory Partnership and honorary secretary of Bilton Conservation Group, said:

The importance of this last point is evident from just a cursory inspection of the river near Skipton Road. Along most of its length, through the countryside to the west and north of Harrogate, the main threats to Oak Beck’s water quality come from sewage outflows and field run-off.

But where it passes through the north-western edge of the town at New Park, it encounters other dangers, such as polluted wastewater from building sites and more obviously, abuse by people using it as a dump. On the day of BCG’s testing, the Stray Ferret saw road signs, shopping trolleys, traffic cones, a steering wheel, and a bicycle in the water.

Once all that has been cleared out and another year has passed, Mr Wilkinson is hopeful that the river will be well on the road to recovery. In the meantime, he remains measured in his assessment, at least until the fish DNA test results come back at some point over the next fortnight.

He said: