The 50m (150ft) pylons would run from Carlisle to Heysham, Lancashire, to connect a new Â£10bn nuclear power plant at Moorside, Sellafield, to the grid.
Power Without Pylons and Friends of the Lake District say the National Grid is "ignoring" demands for the cables to go underground in "sensitive landscapes".
The National Grid said it "fully recognises the importance" of the area.
The campaign walk is taking place from Black Combe where the pylons will be visible, down to the National Park's costal boundary and across the mouth of Duddon.
Graham Pitts, chairman of Power Without Pylons, said: "This is a very serious decision. These pylons are going to be up for the rest of this century.
"I don't think people appreciate two things - one, how stunning the view is around here, and two, how much these pylons are going to affect it by their sheer size."
The Lake District is being put forward as the UK's next nomination for World Heritage status.
A National Grid spokesman said: "We have not yet made a final decision on how and where the new connection will be built.
"When building connections for generators, we strive to avoid designated landscapes. Where this is not possible, we work closely with stakeholders and communities and carry out consultations to develop a proposal which achieves the best possible balance between protecting the environment and ensuring everyone has an affordable electricity supply."
A formal consultation is expected to take place later in the year, with the final plans submitted to the planning inspectorate in 2017.

Two former Welsh secretaries, Lord Peter Hain and Paul Murphy, want to change the law to ensure all candidates are on the Wales electoral register.
Lord Hain said being represented by people who live outside the country was "insulting to the people of Wales".
UKIP's assembly group leader AM Neil Hamilton - who lives in Wiltshire - was asked to comment.
Mr Hamilton was elected on the regional list as AM for Mid and West Wales last May.
At the time Mr Hamilton became group leader he said he lived "less than an hour from Cardiff".
"For the time being I'm living where I lived for the last 10 years," he said, adding there was a "big logistical problem to solve" about where he based himself.
Under current rules there is nothing to stop people living outside of Wales standing as a candidate for the assembly.
The proposed amendment says a person may not stand as a candidate unless they are recorded on the Welsh electoral register as "living in Wales".
Lord Hain said the current rules were an "anomaly" in the Government of Wales Act 2006 - which he said he was responsible for as Welsh secretary at the time.
Lord Hain, who moved from London when he was elected as an MP for Neath, did not criticise Mr Hamilton directly, saying he would not "personalise" the issue.
The Assembly's independent Remuneration Board is considering a change in the rules to allow AMs to claim more than Â£8,000 for Cardiff accommodation expenses if they live in England.
The board - which sets pay and expenses - will discuss the responses to a consultation at a meeting in November.

The university said the move at Singleton Park was "precautionary".
South Wales Police received a call at about 13:30 BST after concerns about the safe storage of chemicals before a controlled explosion took place.
Nobody was injured and a police spokesman said a cordon erected was precautionary while the chemicals were removed.
Student Alex Jones said there was "some panic" at the start of the incident and lectures were moved away from the area to other buildings.
South Wales Police said the incident was not treated as suspicious and there was no risk to the public.
The university said the controlled explosion was carried out by the Royal Logistics Corps bomb disposal unit after the chemicals "had become unstable".

7 July 2016 Last updated at 09:49 BST
Speaking to Today programme presenter John Humphrys, he accepted that in retrospect it would have been better to challenge the intelligence used to justify the war, but stood by his decision to join the invasion.
Campaigners are holding a protest walk against plans to build pylons across the Lake District National Park.
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A bid has been launched to bar people who live outside of Wales from standing for election to the assembly.
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Part of a Swansea University campus was evacuated on Thursday after the discovery of "unstable" chemicals.
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Tony Blair says people will not accept that he means his regret over mistakes in the Iraq war until he disowns the decision to join the US coalition to topple Saddam Hussein.