Fears have been raised that delaying the refill of a drained reservoir could have an impact on wildlife.

The Welsh Harp Reservoir was emptied in December, 2023, with the removal of 400 Olympic-sized swimming pools worth of water revealing a machete, Second World War munitions and even religious offerings.

The water has been lowered to clean up tones of litter and carry out essential repairs, including fixing the chain rods that operate the reservoir’s sluices and repainting the Valve House Tower.

Draining was originally supposed to start in November 2023, but this was delayed.

It was then anticipated that the reservoir would be refilled by the end of February 2024, but the Phoenix Canoe Club, which operates at the site, said in a newsletter that it has heard this could take as long as April.

Times Series: There were around 200 bags of litter in one clean-up event There were around 200 bags of litter in one clean-up event (Image: Canal and River Trust)

This prompted concerns about wildlife that lives and breeds on and around the water.

The club said: “They are now talking April as the refilling date, but this is open ended until the works are started.

“This will have a devastating effect on the club and centre and all of the other clubs that use the water. It will also have an effect on the wildfowl population, as they may start to make nests next to the stream in the middle of the reservoir.

“Currently the gulls, herons and cormorants are having a bonanza picking fish out of the shallow water.”

While the Canal & River Trust has not been able to confirm a date for the refill, a spokesperson admitted progress has been “slower than hoped for”.

Over the next two months or so, there are many tasks that still need to be carried out including completing the fish rescue and draining, clearing silt from the front of the sluices, erecting scaffolding around the Valve Tower, cleaning and repainting the tower, mechanical work to the sluice and rods, removing the scaffolding and only then returning the water.

Times Series: The partially drained Welsh Harp ReservoirThe partially drained Welsh Harp Reservoir (Image: Canal and River Trust)

The trust has said online it shares the concerns of local conservation groups about the impact on nesting birds and it is working with relevant agencies to protect the natural environment.

The trust said: “During a gradual, managed refill, after the works are completed, we will include sensitive and proportionate mitigation measures to discourage birds from nesting on the reservoir margins until it has refilled.”

More than 100,000 fish were removed since work started at the site – some weighing 30lbs each.

Times Series: A massive Mirror Carp was rescued from Welsh Harp Reservoir A massive Mirror Carp was rescued from Welsh Harp Reservoir (Image: Canal and River Trust)

It’s said the total amount of fish removed was 16,000lbs. It will be restocked with native species including roach and perch in the spring and more next year.

A spokesperson for Canal & River Trust said: “Our charity has worked closely with the Environment Agency and Natural England to minimise the impact of essential maintenance work at Brent Reservoir on wildlife and protect the ecology of this Site of Special Scientific Interest.

“Several extreme weather events this winter, coupled with the unprecedented number of fish which have been revealed and rescued, means the process of draining the reservoir is not yet complete.

“We appreciate the impact these statutory works have on activities which normally take place on the water, and we want to see them back up and running as soon as possible.

“While it is frustrating that outside factors have meant slower progress than hoped for, it is vital for the future of this precious wild space that the draining, maintenance work and refilling, is carried out with proper regard to all environmental responsibilities.

“From our crowdfunded and volunteer clean-ups to the installation of bird habitats and removal of non-native species, we are facing up to the environmental challenge and enhancing this site for everyone.”