Provides that such designation shall not be construed to limit the authority of Puerto Rico over waters and natural channels of its public domain or to prevent any of the following activities within such segments: (1) installation and maintenance of hydrologic, meteorological, climatological, or atmospheric data collection and transmission facilities when they are essential to the scientific research purposes of the Luquillo Experimental Forest; (2) construction and maintenance of nesting structures, observation blinds, and population monitoring platforms for threatened and endangered species; or (3) construction and maintenance of trails to such facilities as necessary for research purposes and the recovery of such species. Provides that all such activities shall be subject to such conditions as the Secretary of Agriculture considers desirable. Requires the Secretary to ensure that the scale and scope of such activities are not detrimental to a river segment's characteristics that merited its designation as a wild, scenic, or recreational river.