Power giant RWE npower has refused to confirm it will not restart work at Thrupp Lake until after an inquiry into the area's future.
Save Radley Lakes campaigners are battling to prevent the lake from being turned into a fly-ash dump for Didcot Power Station.
Dozens of protesters last week pleaded with an inquiry to grant town green status in a bid to scupper the energy firm's plans. So many turned up that the inspector considering the application has extended the inquiry to extra days in June.
However, there are now fears RWE npower will carry on with work at the lake and not wait until the result of the inquiry.
The company has said it intends to restart 'major work' once the bird nesting season has finished in mid to late summer.
Jo Cartmell, Save Radley Lakes secretary, said: "We are not sure what is going to happen. We are hoping that npower will cease works."
Save Radley Lakes barrister Philip Petchey said: "This inquiry will adjourn until the end of June.
"The work on the site is currently suspended until the end of the nesting season.
"This is an important public inquiry and if npower is able to say they will not continue works pending the completion of the inquiry and the determination of town green status by Oxfordshire County Council, it would be helpful."
RWE barrister Charles Mynors said: "Npower is concerned over the length of this inquiry, the constant stream of new witnesses and that the inquiry may extend until August or later."
RWE npower spokesman Leon Flexman added: "As things stand, there are preliminary works we can be getting on with during spring and summer that won't change the nature of the area in question.
"We're planning to meet Radley Parish Council soon and will be more than happy to explain these in more detail.
"In the meantime, we'd expect the town green issue to be resolved by the end of the bird nesting season in mid-to-late summer, which is when we plan to resume the major works."
RWE npower would not confirm if major works on the lake would take place before inspector Vivian Chapman made his recommendation to the county council.
Mr Chapman said: "A lot of issues we have discussed have arisen from the complexity of the site. It would be dangerous for all concerned to exclude evidence without great cause.
"A court might well think that Oxfordshire County Council had reached a decision without considering all the evidence."
Andy Boddington, of the Campaign to Protect Rural England, said: "Npower should immediately promise to stop all work at Thrupp Lake until the inquiry has reached a decision."