Nyanza IV

At low tide people swim through Jairnovaunt on the surface, guided by marked buoys. A captain's house contains models, scrimshaw, stuffed fish and a couch covered with the hide of a large sea animal killed by the captain.

We learn the names of three Nyanzan nations:

Jarnovaunt;
The Kraal;
Rossala, which is ruled by a Sheikh.

Uhunhu is a million-year old ruined sunken pre-human city of dolmens and menhirs, used as a base by A'u, a fifteen-meter-long, whale-mouthed, talon-legged amphibian with hands on boneless arms who, like Aycharaych, is not Merseian but serves Merseia and has fought Flandry before although "The Game of Glory" is the only story featuring this particular adversary.

Flandry first meets Aycharaych between chasing A'u out of Spica and catching him on Nyanza. Aycharaych later tells Flandry that his side will miss A'u. We are to understand that Flandry and Aycharaych have clashed between their first meeting and the occasion when the latter mentions A'u. However, we read of Flandry-Aycharaych encounters only in "Honorable Enemies" (the first meeting), "Hunters of the Sky Cave" (mention of A'u) and A Knight Of Ghosts And Shadows (the last meeting). Despite his massive output, Anderson was a restrained author who never overdid anything and later launched new series instead of merely rehashing the Technic History.

In the Kith History, human colonists of a planet with a large ocean became aquatic. Maybe some Nyanzans will do likewise?

Nyanza III

Most parts of Nyanza are permanently underwater, like Uhunhu. However, many of the populated areas are tidal. The domes and towers of Jairnovaunt stand on rocks that are above water at low tide but meters under at high tide. At the latter times, an approaching ship must steer between buoys to an anchored floating dock from which those visiting or returning to the city swim down with aqualungs. On the dock, fish are unloaded, sails are repaired and engines are overhauled while sailors not otherwise engaged make music and dance.

Members of the Jairnovaunt House of Men and Congress of Women are not professional politicians but aristocrats and ship owners with some ship's officers elected to represent the commons. Aristocrats inherit responsibilities. For example, the Lightmistress of Little Skua must maintain lightships and communications around the reef of Skua.

The inner moon raises tides up to nine times a Terran high and orbits five times in sixty hours, thus causing a rapid ebb when water roars and tumbles from rock. The outer moon has a weaker effect without dangerous whirlpools but nevertheless also submerges the city.

Nyanza II

Nyanza:

the third planet of a dwarf star;
colonized during the breakup of the Solar Commonwealth, five centuries before Flandry;
incorporated into the Empire a century before Flandry;
a few revolts crushed;
estimated population 10,000,000;
air smells of salt because of the planet-wide ocean and of ozone because of the strongly ultraviolet sun;
an Imperial resident, a Portmaster, a City Warden and sea chiefs;
most planetography is oceanography, e.g., the Zurian Current turns north beyond Iron Shoals and continues past the Reefs of Sorrow;
plankton-like organisms in the Current change the water from blue to deep purple;
decapus eat oilfish which eat quasi-plankton;
Nyanzans use decapus and oilfish;
the Prince of Aquant's fishing boats, and no doubt others, are identified by their distinctive flags;
sailing boats use engines when the wind drops;
because light is more actinic than on Earth and is everywhere reflected from water, natural selection favors the black skin of the African colonists although facial features may vary;
Nyanzans often go naked;
when the original colonists overflowed the single island, Altla, they began to range the sea and found this lifestyle preferable;
thus, positions newly available on Altla were filled by pinkskins, mostly from Deutshwelt;
this second wave of immigrants could not work at sea where they would get skin sicknesses and cannot be allowed to overpopulate Altla so immigration was halted;
the Nyanzan nations own Altla, employ the Technicians/Lubbers and bar them from owning ships;
Jairnovaunt is a submerged city of domes and towers where a cargo submarine discharges kelpite bails, children with aqualungs play in a coraloid park, an old man feeds fish (not birds) and the hall of the hereditary Commander, Inyanduma III, is surrounded by formal gardens and entered by an airlock after which visitors are dried by an airblast;
Tessa Hoorn, Lightmistress of Skua, reports to the Commander on returning from The Kraal;
when the resident is assassinated and an Imperial investigator is expected, the Commander gathers his chiefs of council from the House of Men and the Congress of Women.

Nyanza

Nyanza is a humanly colonized terrestroid planet with:

two moons;
one ocean;
no continents;
one medium-sized, forested island, Altla;
on Altla, one ancient city with a spaceport, sea docks and an Imperial resident housed in a mansion surrounded by tenements;
many rocks and reefs submerged by high tides;
regularly submerged buildings with airlocks;
an advanced model aqualung with a transparent helmet and a battery electrolyzing oxygen from water and diluting it with compressed helium;
large submarines;
radically hydrodynamic sailing craft;
African-descended Nyanzans fishing, hunting or ranching the ocean; 
caucausoid "Technicians" on Altla processing sea water, sea weed, sea food etc in exchange for metal, fuel, synthetics and engines;
a complex Nyanzan society that will have to be summarized in another post.