Trying to find a book where humans were genetically altered to live in water after a crash landing on a planet. Generations later, they have forgotten they are human. I think the main character is named Levon and he keep swimming to the surface and dreaming of going to the stars.
A human colonization ship crash-lands on a distant planet which is earth-like but whose only landmass is completely covered in shallow puddles of water and mostly microscope life forms. Normal humans could not survive on this planet, so the crew must genetically engineer their descendants into something that can survive. (Blish coined the term pantropy to refer to this concept.) They decide to create a race of microscopic aquatic humanoids to complete their mission and colonize the planet.
The majority of the story concerns one group of these genetically engineered colonists and their intelligence, curiosity, and evolving technology. In particular, the tiny aquatic humanoids develop a "space ship", or rather "air ship", which enables them to pierce the previously impenetrable surface tension of the water and travel through what is, to them, hostile space—open air—to other worlds in other puddles of water.
Here's an illustration for the story from the cover of The Best of James Blish. Nice fig-, erm, algae-leaf!
The guy's name was actually Lavon.