Personally, I doubt that any industrial civilization would have aliens too different from humans. Ultimately tool use breeds civilizations instead of intelligence. Falling from the sky even the most intelligent creature could only calculate how hard they will hit the ground. Same with intelligent aquatic creatures, their use of tools, their metallurgy, their material sciences - all very much diminished. Written word alone would be a giant problem under watter.
I agree tool use affects civilization, but the whole post is one radically different approach to metal using sophonts. :) I do not think the Singers' civilization(s) would be very human-like, driven by the wild biological differences more than the tool using similarities.
Agreed, written word would be difficult, but given clay and stone exist under water, I don't doubt there'd be equivalents of cunieform or Hittite available. Wood, cloth, paper and ink are likely not feasible underwater, but there are other options. Printing presses are likely a VERY advanced technology for those reasons, again causing cultural differences.
Thanks for commenting!