My apologies again for barking last week.

What is a lake?  Good qn.   I am an inclusivist.
I am not very interested in colonial era/Soviet era lakes named from people - e.g. Lake Victoria - E Afr , Lake Nassar Egypt - except to offer a generalization.
The people naming the lakes are underlings , currying favour with the Mr/Ms Big back in the metropolis.
Nevertheless, they are sufficiently high up the pecking order to be able impose their choice of new name.
People named after lakes?   
Maybe Rudyard Kipling (parents honeymooned at Rudyard Lakes STF) and maybe the deer-loving Goidel's "Lady Windermere('s fan"). 

I am interested in the name-pairs formed when places are named after lakes, when lakes are named after places, and when lakes are named after other lakes.    I'd like to suggest some terminology, using examples of name-pairs or patterns from N. Wales, except when it would be pedantic to do so or when there is no NW example. In this case, I'll use examples from the rest of the world.

We can generalize that, in W Europe, lakes are VERY OFTEN often named after the most significant inhabited place on their shores.
Places on the lake shore are OFTEN named after the lake.
Lakes are RATHER SELDOM named after other lakes.   
(Lakes can also be named after rivers - and rivers from lakes - e.g. in Galway/Mayo)  
Lakes are FAIRLY OFTEN named after people (esp. in colonial situations).
People are ALMOST NEVER named after lakes.  (tho' Welsh poets are often named after rivers. Noms de plume, natch.)

How about these type-names:

Lake Bala (NW) Pattern - this is the current English name (though Lloyd-Jones 1928 has "Llyn y Bala")
The lake is named after the most significant inhabited place on its shores.
(purists will point out that the 2nd largest place is LlanuwchLLYN) 
Ultrapurists will point out that, to a speaker of W., "bala" implies a lake.
Lake Geneva/formerly Lac de Geneve

Llyn Tegid (NW) pattern - the lake is not named after the most significant place on its shores.  Nor is the most significant place on its shores (Bala/y Bala) named after the lake.    (purists will...)
Owen & Morgan derive the W lake name from the pers name Tegyd, which is I think from L. "Tacitus" orig.
I would myself see this - maybe - why not? - as from the L. adj "tacitus" - a name like "Lake Placid" NY and FLA - maybe to propitiate some divine lake god.
The English med. name instanced by Owen & Morgan looks as if it is re-interpreted W. (?pen y bal'/ pen Bal' + Eng - mere) and no more referring to pebbles than the durno in Durnovaria does.   
I think I've said this before about these names.

Lac Leman (Lake Geneva) - this is an antiquarian revival of Caesar's Lemannus (form from memory).
It does not - or does not appear - to refer to its most sig. inhabited place - and v.v.
(it might be however that the landscape value of LEM here is the same as that of Celtic GENAUA "mouth" - both here meaning "outflow".  But let's forget this for now)  

LLyn Aerfen (NW) pattern.    This is a former name for the lake - and a former name of the R. Dee, which traverses the lake.
See Owen & Morgan.
I will use it as the exemplar for lakes which are named after the rivers flowing in, out and through them. (Not in my header)
(purists will note that we could also use this type-name  for lakes named after divine figures - see Owen & Morgan)
At least in Ireland, they have rivers named after lakes - but I've mislaid my notes about this, sorry.

Lake Windermere pattern (English Lakes) .    This is the type-name for pairs when the most significant lakeside places is named after the lake.
e.g. Tolkien's "Lake-Town" and "Lake" in the original 1937 ed of "the Hobbit" (he elaborated on these names later).
This seems to be the mode type in W Europe.
We could have a NW exemplar - but only with a marine lake - Pwllheli (=Saltpool) NW.

Llyn Llydaw (NW) pattern - this is the well-known lake near the top of Snowdon/Pen yr Wyddfa. 
For lakes without inhabited places on their shores - so this is necessarily a name-singleton, not a name pair.

Timbuctoo Pattern - is a logical necessity.  Places without lakes.
(Although a nice oasis might count). 

Portsmouth Harbour (HMP) pattern -  when the Lake (here sic) is named from the most sig. inhabited place on its shores - and when as a second condition,-  the town is named from a former name of the lake.    
Poole Harbour DOR.    (Celtic pol, or its OE near-homophone)
 
Lake Nyasa pattern (Central Africa up to 1964).   A very large area - in this case country-sized- Nyasaland, now Malawi - is named after the lake on whose shores it lies.
I believe that "Nyasa" = "lake" in a local language.

Gambia pattern : country/district named after a river.     
Can't think of its v.v. ???

Lake Malawi pattern (from 1960's).   The lake (ex-Lake Nyasa in this case) is named from a country, region, large area etc which borders it.      
I'm not actually sure what "Malawi" means - I suppose it could be another lake ref.
When ignorance is bliss.....
Brittany (W. Llydaw) is not contiguous to Llyn Llydaw, otherwise that body of water would count as a Lake Malawi type lake.
Admittedly, neapoliteiamorphically (see Owen and Morgan).

Interlaken (CH) Pattern - lake-shore place is named after more than one lake.
Baladeulyn NW - wherever it exactly is (p. 96 in Lloyd-Jones)
 
Lake Superior (N Am) pattern.    The lake is implicitly or explicitly named referencing another lake/other lakes.
Lago Maggiore.
I would have liked to call this type "Carlow pattern" (Leinster) - because Joyce and his successors define this as "quadruple lake, 4 lakes". (Ir Cetherloch).   "Of which, however, there is no trace" PWJ vol 1 p. 433
Adrian Room op cit mentions a confluence of rivers - so I of course wonder whether this might not be the original landscape observation.

There is a Loch Idir 2 Loch - form from memory - just to the W. of Galway on the 1 50000 map (Ord Survey of Ireland).
This means "Lake between 2 Lakes" - and sure enough it is the middle lake of three.

Thanks for reading this post.
Nick