In the case of Idaho ex rel. Andrus, Governor, et al. v. Oregon et al., 1976, the U.S Supreme Court was asked to resolve a dispute between states over fishing rights in the Columbia River and its tributaries. The state of Idaho argued that it should be allowed to regulate fishing on these waters because they flowed through its territory; however, Oregon and Washington claimed that they had historical rights to manage fisheries there based on longstanding practices and agreements among Pacific Northwest states. The court ruled against Idaho by upholding an earlier decision from a special master who found that Oregon and Washington had established their authority over these fisheries through "original understanding" or customary usage dating back many years before Idaho became a state. This ruling affirmed the principle known as equitable apportionment which holds that when multiple jurisdictions have claims to shared natural resources like waterways or fish stocks, courts will seek fair solutions based on factors such as historic use patterns rather than strict territorial boundaries.

In the dissenting opinion for Idaho ex rel. Andrus, Governor, et al. v. Oregon et al., Justice William Rehnquist disagreed with the majority's decision to uphold a lower court ruling that allowed Oregon and Washington exclusive rights over fishing in certain areas of the Columbia River. He argued that this was inconsistent with previous Supreme Court decisions which had held that no state could claim ownership or control over migratory fish in navigable waters because they were considered an interstate resource under federal jurisdiction. Furthermore, he contended that granting these states such authority violated principles of equal footing by giving them more power than other states to regulate natural resources within their borders.