A bi-annual survey of water quality in our rivers and streams has revealed an improvement in the quality of one town-centre watercourse - although elsewhere the picture is unchanged.

Pollution testing of the River Len in Maidstone carried out as part of the Great UK WaterBlitz, has revealed that over the past six months, nitrate and phosphate levels have dropped at the Palace Avenue mill pond alongside Len House in Mill Street.

The results will be good news for the new residents who will be moving into the art deco building, once home to the Rootes Motor Garage, and currently being converted into 159 flats by Classicus Estates.

Nitrate levels at the mill pond indicated contamination of between 2 and 5 mg per litre - a big drop on the last survey findings from September last year, when they registered between 5 and 10 mg per litre.

Phosphate readings from the mill pond were also slightly reduced over the 2024 readings from just under 0.2mg per litre to just over 0.1mg per litre.

The samples were taken during the citizen science water testing event organised by Earth Watch, which took place over the past weekend.

More than 57,000 volunteers took part.

Tony Harwood took the Len water samples. He is the chairman of the River Len Local Nature Reserve Management Committee. The reserve sits alongside the Len, just up from the Sainsbury car park in the town centre.

He said: “The improvement is likely down to prevailing drier conditions reducing levels of surcharging sewage from combined overflows, less contaminated rainwater runoff from upstream roads and other contaminated land and also the recent interventions by Southern Water to tackle wastewater ‘misconnections’ in the town centre.

“A clean-up of the mill pond itself by contractors, MBC personnel and volunteers has also helped by removing large quantities of sewage rag and by increasing flow rates.”

“But,” said Mr Harwood, “less positively, and perhaps counterintuitively, testing on an upstream stretch of the River Len at rural Otham revealed higher nitrate contamination levels than those seen in the town centre.

“The test site at Otham came in at the upper end of the 5 to 10mg per litre scale.”

“Fewer aquatic invertebrates and fish were also observed at Otham than were seen at the mill pond by the former Rootes building.”

Mr Harwood said: “This difference is likely explained by the proximity of the Harrietsham Treatment Works, which discharges into the Len, and nutrients leaching into the river from upstream agricultural land.”

But Mr Harwood was encouraged.

He said: “These latest test results show that concerted action to clean up and restore our rivers can make a difference.”

Elsewhere, the Loose Stream also showed high levels of nitrates when tested both in Loose and further downstream at Tovil. The phosphates levels were slightly lower at Tovil. Both results were similar to last September.

At Yalding, the River Beult gave two very different readings at testing spots only a short distance apart.

The upstream testing point recorded nitrates of between 1 and 2mg/l, while a few hundred yards downstream they were between 5 and 10mg/l.

The River Medway showed a relatively low nitrate level just upstream from the town centre, and then constantly higher levels, as the river flowed through the town.

The outflow of the River Len from the lake in Mote Park was also among the highest spots for nitrate pollution.

The lake is home to many ducks and geese, but is also used by the public for sailing, paddleboarding, kayaking and - most recently - water-biking.

Both high nitrate and high phosphate concentrations encourage phytoplankton growth, which reduces light penetration into the water. This process, known as eutrophication, reduces the oxygen available for fish, crustaceans and other aquatic wildlife.

Some algal blooms also produce toxins that can be harmful to both wildlife and humans.

Volunteers are still reporting the results of their UK WaterBlitz findings, and a live map of the readings can be viewed here.

The results will be assessed by Earth Watch and a full report will be published in a month or two’s time.