The building of the Welsh Harp wetlands

Professional ornithologist and biodiversity expert, Leo Batten co-founded the Welsh Harp Conservation Group in 1972, and has been instrumental in work to preserve the Welsh Harp’s SSSI status ever since. Now a cornerstone figure at Cook Oak, he looks back on the major wetlands redevelopment that he helped instigate in the late eighties.

As with any urban lake and surrounding open space, there will be a great demand to use it for recreational activities. It can be a considerable challenge to cater for all these and other interests. The Brent Reservoir, or the Welsh Harp as it is more locally known, is no exception. 

This site however, is one of the oldest Sites of Special Scientific Interest in England, having been notified in 1950 - just a year after citations began - primarily for its breeding and wintering waterbird populations. The fact that it is still an SSSI in an ever-congested urban area is due in no small way to the long-term dedication and work put in by volunteers over the decades, aided by grants from a variety of organisations particularly in the 1980s and 90s.

From the 1950s onwards, as interest in sailing and canoeing at the Welsh Harp continued, it was important that the wildlife - particularly waterbirds - were able to find refuge areas and suitable undisturbed nesting sites while the sailing took place. The ideal locations were the areas of the reservoir around the mouths of the inflowing River Brent and Silk Steam where deposits of silt and the natural shallow sloping margins have resulted in a variety of wetland habitats - open water, fen, reedbeds, willow carr and wet woodland. 

Without human intervention, however, such habitats will - by natural succession - slowly transform into a monoculture of wet woodland which will not support good species diversity, and by the 1980s this is what had happened at the Welsh Harp.

A programme of re-profiling was required.

Beginning in 1985, the work was carried out using earth-moving tracked hydraulic vehicles and an Aquacat - a barge fitted with a bucket and hydraulic arm, which can penetrate areas where land-based machines would not be supported.

The north marsh open water areas were extended back two hundred metres by the removal of silt and the creation of a channel and two large pools with islands. Several refuges were created in both the east and north marsh, by partially cutting off access to the waters edge with canals and resultant additional islands.

The same machinery transplanted large chunks of reed to create reed bed extensions. In addition, a Mudcat suction dredger was used to remove some 12-15 thousand cubic metres of silt in order to make the refuges deeper in places, and to create a better balance of open water to marsh. The dredger sucked up the silt from the reservoir bed and pumped it though long pipes, releasing it into settlement lagoons or ‘bunds’ built on the dry land nearby. These are now recolonised by woodland. 

Willows were also removed from the main island in the east marsh at the mouth of the River Brent, and eighty tons of shingle were brought on by the Environment Agency to create a wader scrape and loafing area for ducks.

Screening the birds from the increasing water sports was also important, and twenty-four nesting rafts were created across the water in front of the east marsh. These provided safe nesting sites which would rise and fall with the water level. A colony of Common Terns subsequently became established as a result. Later, three much larger nesting rafts were added made from an old jetty donated by the sailing association, and another six were constructed, bought with money from the Heritage Lottery Fund.

Persistent lobbying against pollution and rubbish entering the reservoir also resulted in the construction of trash screens and surface booms on the River Brent and Silk Stream. The automatic trash screen on the Silk Stream, which opened with an official ceremony, started functioning in the spring of 1989. Both reduced the amount of rubbish and oil entering the reservoir, but in recent years, due to funding cuts, the Environment Agency have not been able to empty them regularly, resulting in significantly increased rubbish and oil entering the reservoir.

Much of the management was made possible by grants to the Welsh Harp Conservation Group from the then Greater London Council, Barnet Council, Brent Council, English Nature and the Heritage Lottery Fund.

Today, more re-profiling - in particular the thinning out of recolonised vegetation around the reed beds and on the wader scrape and replacement of the ageing breeding rafts - is urgently needed, and the new reservoir owner, Canal and River Trust is now providing funding and contractors to start this work in the east marsh. 

Unfortunately, Barnet Council - ignoring valid conservation objections - has given planning permission for a large footbridge to be built over the centre of the north marsh wetlands in 2023. This will destroy the marsh as an effective refuge and severely damage this part of the SSSI, without apparent reasonable excuse. If the bridge cannot be stopped, it is imperative Natural England demand maximum ecological mitigation measures and commensurate biodiversity gain as close to the North Marsh as possible. It is a battle Cool Oak are still fighting.