Two UK giants of nature broadcasting have clashed over how tourists should best enjoy the Galapagos Islands.
Prof Bellamy (left) was described as misguided by Sir David
Professor Bellamy, president of the Galapagos Conservation Trust, wants a monorail built to take visitors around and bring in some much-needed money.
But Sir David Attenborough said that would "destroy the islands" and thinks the existing boat service works well.
A trust spokeswoman said the idea was Prof Bellamy's "personal opinion" and not an official trust plan.
The 12 islands are 1,000km from the coast of Ecuador and internationally recognised as a key centre of conservation.
They have many native species and were crucial in the development of Charles Darwin's ground-breaking theory of evolution.
Prof Bellamy told BBC Radio 4's Today programme the islands were "strapped for cash".
"This is the 21st Century, we have got to get some 21st (Century) answers," he said.
"I do actually think a skyrail put in the right place would put a lot of the money in and save the problem."
He praised mass tourism, which "if it is done properly, is doing marvels around the world".
However, Sir David described his "old friend" as "absolutely misguided".
"I believe that a monorail wouldn't bring the benefit and would actually more
or less destroy the islands," he said.
He said tourists would spend more cash on the cruise ships they arrived on, than the islands themselves.
The current practice of taking visitors around the islands in small boats was "absolutely perfect" as it gave visitors a better appreciation, he added.