I come late to this discussion but, being an oceanographer (and to a lesser extent a limnologist), I am well used to the adjective oceanographic and noun oceanography, with the corresponding freshwater equivalents limnological and limnology.
With that in mind, oceanic refers to oceans, bodies of marine water (typical salt content 3.5%), whereas limnic refers to bodies of relatively low or zero salt content.
A reliable non-technical definition of limnic is given by Collins:
relating to bodies of water with low salt concentration, such as lakes and ponds
The adjective limnic therefore applies to rivers, lakes, streams and other volumes of fresh or near fresh water and is not a word confined to lakes.
Hence, limnic and its associated words (limnology, limnological) include lakes but are not restricted to them.
Two alternatives remain: limnetic and lacustrine
of, relating to, or inhabiting the open water of a body of fresh water
Merriam Webster exemplifies the commonly understood definition of lacustrine:
of, relating to, formed in, living in, or growing in lakes
There is a comprehensive literature that uses the word. See for numerous examples too many to quote here:
Of these two possibilities, the prime candidate specific to lakes is thus lacustrine
And that is why I voted for the relevant earlier answer.