Hi: there are two lakes in the city of Lake Forest: Hidden Lakes (which used to be called Lake One) & the Lake Forest Keys (which used to be called Lake Two). Before the city was incorporated as Lake Forest it was comprised of two un-incorporated areas: Lake Forest which comprised the two lakes & all the homes that belonged to those lakes and El Toro which comprised thousands of other homes that did not & could not belong to either lake. Since then the areas called Foothill Ranch & Portola Hills have been incorporated into the city of Lake Forest (although most people still call those two communities by their original names).
In any case, only the few thousand homes (including detached homes & condos) that originally belonged to either of the two lakes can belong to the lake. And it is the home that belongs; in fact, once a home belongs to the lake it can never not belong to the lake, which means that current owners must pay the association dues that go along with lake membership whether they use the lake or not: it is called running with the deed.
So, buying a home in Lake Forest which belongs to the lake, will make those homeowners members of only that lake (no home belongs to both lakes). And, buying a home which does not belong to either lake means the owners can not belong to either lake not even by offering to pay a fee to do so.