In any case not otherwise provided for in this subchapter, the
Secretary shall be prohibited from condemning any commercial
property used for commercial purposes in existence on December 31,
1964, so long as, in his opinion, the use thereof would further the
purpose of this subchapter, and such use does not impair the
usefulness and attractiveness of the area designated for inclusion
in the lakeshore. The following uses, among others, shall be
considered to be uses compatible with the purposes of this
subchapter: Commercial farms, orchards, motels, rental cottages,
camps, craft and art studios, marinas, medical, legal,
architectural, and other such professional offices, and tree farms.