In my article "Summary judgment in irrigation case cause for celebration with caution," I said:
At last, due consideration was given to the fact that Congress specifically authorized irrigation dams on the Yellowstone River. The Intake dam was authorized by Congress. The Endangered Species Act was passed afterwards. This lawsuit attempts to apply the ESA retroactively or as if the passage of ESA repealed the earlier authorization of the dam. In this new order, Judge Morris puts the kibosh on that. He recognized that a second act of Congress must show a clear intention to repeal a prior act, or else the authorization continues.
That act of Congress is 58 P.L. 209, 33 Stat. 1045, 58 Cong. Ch. 1476, 58 P.L. 209, 33 Stat. 1045, 58 Cong. Ch. 1476, Codified at 43 USCS § 422.
Following is an image of this law taken from my set of reclamation law books.