Amphibious Cycle: Powered On Water By A paddle Wheel (Video)
The designers say the machine could be used to deliver aid to flood-hit areas.
The trike is the final project of seven students from Southampton University's School of Engineering.
The students began working on the project in October - eight months before mechanical engineering student David Edwards finally took to the water to test the cycle.
Mr Edwards, 22, said: "When the cycle hit the water it was a very proud moment.
"It certainly raised a smile from everyone who saw it.
"All seven of us worked so hard on the project, and it was brilliant to see everything working perfectly.
"There are other amphibious bikes on the market, but the one we have designed is unique because it uses floats, a paddle wheel and the rider sits in a recumbent position.
"Also, the transition from land to water is completely seamless which is very rare."
The amphibious trike was tested on the River Itchen next to the university's sailing club in front of a crowd of 35 people, all invited by the students.
Mr Edwards believes the cycle could have a wide range of uses.
He added: "The cycle could be used for humanitarian aid to carry water or food across flooded areas.
"The UK isn't immune to flooding so it could also be used closer to home.
"I think holiday centres could also be interested.
"The cycle will be on show at the Southampton Boat Show, so that might just be the perfect launch pad for the product."
The students, from a range of subjects including ship science, construction and mechanical engineering, were set the project as part of the final years of their degrees.