The case to expand the size of the Lake District National Park is the strongest of any of the parks around the UK, the man leading the bid says.
The proposal, submitted by Friends of the Lake District, would add about 155 sq kms, or 6% to the park's size.
It would include land between Silecroft to Grange-over-Sands as well as the Cartmel peninsulas.
Natural England said it was reviewing its approach to designating and varying national parks.
Campaigners backing the proposal, such as the Southern Boundary Partnership, believe the new areas would benefit from extra protection and increased tourism.
Douglas Chalmers, chief executive of the Friends organisation, believes previous recent expansions of other parks has strengthened the case, according to the Local Democracy Reporting Service.
"We did our work on this during the summer and now we are putting our application to Natural England to make things happen," he said.
"We said already to the prime minister there is [also] historical precedent for this version of the national park when the lines were first drawn in the 1940s."
'Front of the queue'
The estuaries of the rivers Duddon, Leven and Kent, and Millom Without, would be incorporated into the national park if the scheme is approved.
The plan comes four years ago after boundaries were extended into the foothills off Yorkshire and Lancashire and last month Prime Minister Boris Johnson announced a plan to protect an extra 400,000 hectares of English countryside, by 2030.
"The areas we want to extend into at Silecroft and Grange-over-Sands were meant to be in the national park originally," continued Mr Chalmers.
"There are other areas in the UK also going for this, but we think we have the strongest case. We think we will get to the front of the queue."
A spokesperson for Natural England said: "Natural England is reviewing its approach to designating and varying National Parks in the light of the recently published Glover Landscape Review.
"We want to ensure that future landscape designation work adds value to existing family of designations, ensuring national landscapes are key in tackling the joint challenges of climate, nature and wellbeing, as well as the conservation of landscape beauty."