The planning application for an ‘Activity Hub’ at Thirlmere - which includes several zip wires across the lake itself, has been submitted to the Lake District National Park.
Tree Top Trek also wants to set up an 18km ‘family friendly’ cycle way in the area.
The plans are currently out for public consultation, with any responses to the Lake District National Park Authority needing to be submitted by the 2nd of January.
Laura Fiske, planning officer at Friends of the Lake District - who are against the plans, said: :If approved, this application would have significant harmful impacts on the landscape and tranquillity of the Thirlmere valley.
"Fundamentally we consider that introducing commercial activity into this area would be at odds with the reasons for the designation of the Lake District, as it conflicts with laws and planning policies that protect the spectacular landscapes of our National Parks.
"The development would also create an unacceptable precedent – if approved it would open up the whole Lake District National Park and other national parks to inappropriate development.
"National Parks are for everyone to enjoy not just those who can afford to participate in so called adventure experiences."
A Treetop Trek spokesperson said: "Our aim is to create a family friendly, world class visitor attraction combining adventure, leisure and the spectacular Lake District landscape with minimal impact on the surrounding environment.
"Located at Thirlmere reservoir, the proposed Hub will enable more people to enjoy the breath-taking scenery and be active outdoors via two exciting new activities: a thrilling quadruple 1200m zip line across the water and 18km of superb family-friendly cycle paths.
"Working with our friends at ZipWorld, we aim to create a truly amazing outdoor experience. The almost invisible wires will fly visitors twice over the water from dizzying heights up to 130m above the ground, 1200m across, making it the highest and longest zip line in England.
"Being very mindful of the surrounding environment, our take-off and landing stations will be sympathetically constructed within the managed forestry and located to minimise the visual impact and our footprint on this important landscape."