Draining of the Brent Reservoir in North London to complete urgent repair works has revealed a "secret river" and tonnes of rubbish.
Around 400 Olympic-sized swimming pools worth of water has been drained from the reservoir as part of a £2 million project by the Canal and River Trust, a national charity that looks after the site.
Also known as the Welsh Harp, due to its resemblance to the musical instrument, Brent Reservoir was built in 1835 to supply water to the Grand Union Canal.
It is a Site of Special Scientific Interest (SSSI) due to the birds breeding in the surrounding wetlands, as well as being home to 16 protected plant species.
In October 2023, the Canal and River Trust began a five-month project to repair the sluice gates, which control the water levels in the reservoir.
A "secret river", called the Silk Stream, has been uncovered after the drainage of around one million cubic metres of water, which took around four weeks to complete.
Drainage also provided a "unique opportunity" to remove tonnes of rubbish that has been dumped over the years.
The trust set up a crowdfunding campaign which aims to raise £15,000 to fund the removal of "tonnes of litter" that has been washed or dumped into the water.
The site is frequently a victim of fly-tipping and rubbish also enters the reservoir via the River Brent and the Silk Stream.
The Canal and River Trust's director for London and the South East, Ros Daniels, said: "Local wildlife is fighting a constant battle against plastic pollution and fly-tipping from external sources.
"Over the years our reservoir has filled with rubbish, threatening the health of water birds and all the wildlife that makes its home here.
"But now we have a unique opportunity, while the reservoir is drained for maintenance work, to clear up the reservoir for both nature and people."
During the draining process, around 100,000 fish were rescued - including a massive mirror carp which shocked two contractors brought in to carry out the work. Rescued fish will be rehomed in "nearby canal locations".
When work is complete, the sluice gates will be closed to allow the reservoir to refill, which is expected to take between two and four weeks. The whole project is expected to be finished by March.
The Canal and River Trust national fisheries and angling manager John Ellis said: "When the reservoir has refilled with water, we plan to restock it with native fish species, including roach and perch, beginning in the spring and completed next autumn and winter."
