The Duke of Sussex has pleaded with corporate oil drillers not to “pillage the ecosystem for potential profit” as he launched a new environmental campaign.

       In a joint opinion piece for The Washington Post, the Duke and activist Reinhold Mangundu described the Okavango River Basin in southern Africa as a “natural beating heart that has nourished humans and wildlife for generations”.

       The opinion piece is part of the Duke’s campaign with conservation group Re:wild.

       The Duke and Mr Mangundu said they had both “found sanctuary and inspiration in the Okavango” and “said that some things in life are best left undisturbed to carry out their purpose as a natural benefit. This is one of them.”

       They highlighted an oil spill off the coast of California earlier this month and a fire on the ocean's surface off the Gulf of Mexico in July, saying: “There is no way to repair the damage from these kinds of mistakes.

       “Drilling is an outdated gamble that reaps disastrous consequences for many, and incredible riches for a powerful few.

       “It represents a continued investment in fossil fuels instead of renewable energies.”

       They accused ReconAfrica, a Canadian oil and gas company that undertaking exploratory drilling in Namibia and Botswana, of keeping the river basin “under siege”.

       The Duke and Duchess of Sussex earlier this week announced they were becoming “impact partners” with an asset management company that they said invests ethically, but it was reported on Thursday that the firm invests in fossil fuels.

       According to the Daily Mail, Ethic holds shares in multiple oil and gas companies, a number of airlines and some of the world's largest manufacturers, such as General Motors and Honda.

       The Sussexes have not disclosed which companies they have invested in and were approached for comment.

       An Ethic spokesman said: “We allow our clients to choose the environmental, social and governance issues that are most important to them and then help them create custom portfolios based on their preferences – not ours. Your personal portfolio might look different from your family members' or friends' that prioritise different things.

       “If you indicated something like poverty as a primary concern, of course certain pharmaceutical companies would be flagged for removal (and they are for many of our clients due to drug pricing issues).”

       The Duke has regularly spoken out about climate change issues.

       On Thursday he called on governments to do more to protect the environment from companies pursuing profit from fossil fuels in Africa.

       The Duke and Mr Mangundu said: “To protect the Okavango River Basin, we call on the world to stand in solidarity with us, our allies and local communities in advocating a full moratorium on oil and gas development in the region.”

       They added: “Now, the choice is simple: Either we honor our natural and life-sustaining ecosystems, preserving them for generations to come, or we exploit them on a path to permanent destruction.

       “Will you stand with us?”

       The delta is one of the largest freshwater wetlands in southern Africa, the main source of water for a million people, and one of Africa's richest places for biodiversity.

       Ahead of a visit to the region in 2019, Harry said in an Instagram post from his official account: “Known by the locals as 'source of life', this ecosystem is wilderness at its best, playing an absolutely crucial role for the planet, people and wildlife. This is our one and only chance to save this magnificent last Eden.”