I borrowed this novel from my local library several years ago. Set on a waterworld, it has genetically modified aquatic humans who are now in conflict with the original plan to terraform it. Any ideas? I can't remember title or author and have googled to no avail.
The background is that the standard colonisation pattern for not quite Earth type planets are initially colonised by genetically modified humans as terraforming is begun, but as this reaches its final phases the altered humans are phased out. However on this planet they are trying to challenge the process.
The people aren't radically altered, no gills or tentacles! Just a bit plump, and better swimmers, more like Selkies than mermaids.