I saw this interesting news story:
A new study published in The Monthly Notices of the Royal Astronomical Society suggests that most habitable planets are wet. Like, extremely wet. Using computer models, astronomer Fergus Simpson from the Institute of Cosmos Science at the University of Barcelona found that habitable exoplanets, at least simulated ones, tend to be overrun by water, in most cases accounting for 90 percent or more of the total surface area.
Being a science fiction fan of a certain age, the story immediately called to mind James Blish's classic short story Surface Tension, which you can find in The Science Fiction Hall of Fame, Vol. 1: 1929-1964, in which space scientists stranded on a water world genetically engineered their miniaturized descendants (more or less) to live underwater. It's a great story. Go read it.