The John Muir Trust, which is opposed to plans from Scottish & Southern Energy, said routing the new power line along the seabed would make it easier to connect to new offshore wind farms.
Scottish & Southern wants to build 600 pylons, up to 64m high, through the Cairngorms National Park. This would connect new windfarms near Inverness to Glasgow and Edinburgh.
The power link proposal has been the subject of a one year planning inquiry called by the Scottish Executive after 18,000 people formally objected to the plan. The inquiry - the biggest ever held in Scotland - closes next week.
Scottish and Southern Energy has so far argued that overhead power lines are the only viable way of constructing the power link. "The public inquiry is the forum in which the debate must now take place," said a spokeswoman for the power company.
The Scottish Executive is expected to make a decision on the power line next year.