People navigate with the electric boat SunWave catamaran, on the Mediterranean sea during the Les Nauticales boat show, on March 26, 2019 in La Ciotat.

Green investing in marine-related activities such as sustainable fishing and ocean-based tourism is a "pretty exciting" opportunity, according to one Credit Suisse executive.

"It's pretty exciting. If you calculate ... the oceans in an economic term, it is the seventh-largest GDP in the world ... It includes sustainable fisheries, it includes tourism that's based on (the) ocean and it includes all of the other investments that go into seventh-largest. So, people aren't really aware of that," said Marisa Drew, CEO of the impact advisory and finance department at the investment bank.

Speaking to CNBC on Wednesday at the Credit Suisse Asian Investment Conference in Hong Kong, she added: "We're seeing of course pollution issues, warming of the oceans ... overfishing, and our clients and investors really deeply care about trying to resolve some of these issues. So they're saying: 'How do I take this passion for the oceans and find an investible format?"

The World Bank defines that so-called "Blue Economy" as "sustainable use of ocean resources for economic growth, improved livelihoods and jobs, and ocean ecosystem health." Some examples include sustainable fisheries, maritime transport and better waste management.

Another "great investment theme" would be green technology, into which "an enormous amount of investment" is going into, according to Drew.

She cited China's ambitions to become the world's leader in green technology as well as Beijing declaring that the country was going to "ban petrol cars in a very defined period of time" in its move towards electric vehicles.

"If you think about that, it's a market segment that gets created from zero to hundreds of billions in just a couple of years," Drew said.

According to Drew, that kind of sustainable investing can serve as a safeguard for investors

"A lot of our investors are actually looking at this as uncorrelated to general market cycles and increasingly also, in sustainable investing, what we're seeing is academic research coming out that shows if you have an (environmental, social and governance) strategy as an overlay to your investments, it actually dampens down volatility in times of market shocks," Drew said.

That, she said, makes the sector "quite attractive to investors when they are seeing troubled times."