"I'm happy and proud of the Flipflopi team. This is a key innovation around the blue economy. It's also a message to leaders across the globe on environmental issues," he said.

Kazungu challenged young people to ensure they are part of the ocean clean-up, as well as to use the waste to come up with innovative products.

Ben Morison, co-founder of the Flipflopi Project, said he was overwhelmed by the level of engagement during the expedition.

"The reception — from school children to local, regional and national governments — has been nothing short of incredible. Five thousand school children turned up. This historic expedition really has started to turn the tide on plastic," he said.

Morison said 17 hotels in Kenya's coastal city of Mombasa promised to ban single-use plastics bottles and drinking straws.

"We just created a background environment for the private sector to step up. It's also encouraging the City Council of Mombasa closed the Kibarani dumpsite. We are proud to be a key component in making change happen," he said.

Morison said the expedition was about engaging people to change their mindsets and act on single-use plastics.

Challenge was part of the expedition as well. Morison said it was a voyage to the unknown.

"When you depart on a journey using a sailboat that has never been made before, you don't know how it will react. To our amazement, it sailed incredibly well. We traveled over 500 kilometers. We encountered big waves and winds. We were scared — but on down tide, the dhow sailed incredibly well," he said.

Morison said people in Zanzibar are already inquiring the Flipflopi team on how to make a similar vessel. "We are sharing ideas and knowledge with them, hoping more people will get useful information to recycle plastic waste," he said.

Ali Skanda, the FlipFlopi project's chief boat builder, said their successful expedition to Zanzibar gave them confidence their dream to build a bigger boat is achievable.

"We are happy we were able to deliver our message during the voyage to communities and schools. We want them to understand the plastic bag problem," he said.

The Flipflopi expedition left the Kenyan Island of Lamu on Jan 23. Along the way, the crew docked at six Kenyan and Tanzanian coastal towns.