The visitor centre is being replaced and a new nature reserve created
Work to more than double the size of Abberton Reservoir, near Colchester is well underway.
The plans involve flooding the surrounding land and Essex Wildlife Trust Visitor Centre and the B1026.
"We have 2km of road to divert and a new road to lay," said Essex & Suffolk Water's Jim Jenkins.
The project has been 15 years in the planning, the practical work began in January of this year, with targeted completion for the end of 2013.
Since work began five months ago, good progress has been made on the site.
"The weather has been quite good to us moving earth about, and we are on target to meet all our deadlines," he added.
The aim is to increase the volume of the reservoir by approximately 60%.
"Our planning figures show that there is a constant increase in water need in the area," said Jim.
"We're looking 20-30 years in the future, so we needed this reservoir now to meet that demand.
"Also we have to take into account the issue of climate change, which shows we are having wetter winters and drier summers," he added.
Since 2002 the Essex Wildlife Trust have planted 25,000 trees
"So we need to be able to capture more water in the winter and store it for summer use."
Essex Wildlife Trust
senior warden Jo Wray said they were really sad to lose the visitor centre.
"We've actually outgrown the use of the visitor centre for a quite a few years now," said Jo.
"We're really excited because
Essex & Suffolk Water
are going to be replacing our visitor centre on higher ground."
They have also been busy creating a new nature reserve.
"We've put lots of new footpaths in, the walks are just spectacular at the moment," Jo added
The Trust believe it will take another 10 to 15 years before the reserve is back to what they currently have now.
"With new woodland, it's obviously going to be a while before it is up and running," said Jo.
"I'll probably be up here when I'm about 80, 85 looking at it thinking that it's just about looking right [the woodland] by then."