The Alatna River is one of the six federally designated wild and scenic rivers partially contained within the boundaries of Gates of the Arctic National Park, Alaska. It is called one of the most beautiful rivers in the United States.
What is the precise meaning of scenic and wild here? (source)
It looks like it's a classification from the US government. Related to an act of the US congress to protect and preserve US rivers.
River Classification
Rivers are classified as wild, scenic, or recreational.
Wild River Areas – Those rivers or sections of rivers that are free of impoundments and generally inaccessible except by trail, with watersheds or shorelines essentially primitive and waters unpolluted. These represent vestiges of primitive America.
Scenic River Areas – Those rivers or sections of rivers that are free of impoundments, with shorelines or watersheds still largely primitive and shorelines largely undeveloped, but accessible in places by roads.
Recreational River Areas – Those rivers or sections of rivers that are readily accessible by road or railroad, that may have some development along their shorelines, and that may have undergone some impoundment or diversion in the past.
Regardless of classification, each river in the National System is administered with the goal of protecting and enhancing the values that caused it to be designated. Designation neither prohibits development nor gives the federal government control over private property. Recreation, agricultural practices, residential development, and other uses may continue. Protection of the river is provided through voluntary stewardship by landowners and river users and through regulation and programs of federal, state, local, or tribal governments.
These aren't terms defined by U.S. Legislation. Common English here, but precise.
Wild is an ecological term, which probably references the lack of human impact in these areas. Human impact of any kind is absolutely prohibited in most federal and state parks in the united states. Wild is often used as the inverse of domesticated which refers to things that have been so heavily influenced by humans that their essence changes.
Scenic probably means that it has facilities for tourists. There are probably hiking trails, overlooks, a visitor's center, etc. Not sure about this one, it could also refer to how the beauty of the area attracts tourists.
Actually, those terms are defined by U.S. legislation. As noted earlier, when a river is designated into the National Wild & Scenic Rives System, it is given one of three classifications for management and protection purposes -- wild, scenic, or recreational.
Wild River Areas – Those rivers or sections of rivers that are free of impoundments and generally inaccessible except by trail, with watersheds or shorelines essentially primitive and waters unpolluted. These represent vestiges of primitive America.
Scenic River Areas – Those rivers or sections of rivers that are free of impoundments, with shorelines or watersheds still largely primitive and shorelines largely undeveloped, but accessible in places by roads.
Recreational River Areas – Those rivers or sections of rivers that are readily accessible by road or railroad, that may have some development along their shorelines, and that may have undergone some impoundment or diversion in the past.
These are defined in Section 2(b) of the Wild & Scenic Rivers Act, Public Law 90-542.
BTW: This answer was written by a member of the Interagency Wild & Scenic Rivers Council, so this should considered the definitive answer.
Scenic River Areas – Those rivers or sections of rivers that are free of impoundments, with shorelines or watersheds still largely primitive and shorelines largely undeveloped, but accessible in places by roads.
Recreational River Areas – Those rivers or sections of rivers that are readily accessible by road or railroad, that may have some development along their shorelines, and that may have undergone some impoundment or diversion in the past.
Section 2(b) of the Wild & Scenic Rivers Act, Public Law 90-542 was there all along. What about that citation doesn't satisfy you?