He starts the role immediately at the small ship cruise aggregator after joining from The Internet Traveller which he co-founded.
Clark said: "With an already extensive network of business relationships around the world, I anticipate a smooth transition into the role.
"I am really excited by the company’s plans for future growth and development, and the group’s commitment to joint marketing activities across the globe."
eWaterways Cruises chief executive Soren Langelund added: "We are absolutely delighted that Charlie has joined us. His depth of experience and standing in the UK market will serve our company well.
“We are confident that with him at the helm we will see significant growth in the UK, which we believe is the perfect market for this product. eWaterways plugs a serious gap in the market by offering worldwide small niche cruises in fantastic locations, on one website.”