köl

/ køl /

Cases

SingularPluralWhen to use it
nominative köl the lake kölle the lakes the plain dictionary form — the doer of the sentence
genitive kölnü the lake's kölleni the lakes' the owner — whose it is
accusative kölnü the lake (as the object) kölleni the lakes (as the object) a specific, known object — whom or what
dative kölge to the lake köllege to the lakes direction or recipient — to where, to whom
locative kölde at / in the lake köllede at / in the lakes where it is; also having — mende bar, "I have it"
ablative kölden from the lake kölleden from the lakes where it comes from; also "than" when comparing

The endings are the same ones the pronouns wear — that page explains when each case is used.

With an owner

One ownedSeveral owned
my kölüm my lake köllerim my lakes
your kölüng your lake köllering your lakes
his / her kölü his / her lake kölleri his / her lakes
our kölübüz our lake kölleribiz our lakes
you all's kölügüz you all's lake köllerigiz you all's lakes
their kölleri their lake kölleri their lakes

The overlap in the last rows is real, not a mistake: kölleri can mean "his / her lakes", "their lake", or "their lakes" — context decides.