In the case of Texas v. New Mexico (1979), the dispute revolved around water rights to the Pecos River, which flows through both states. The U.S Supreme Court was asked to resolve a disagreement over an interstate compact - an agreement between two or more states approved by Congress - that had been signed in 1948 and aimed at equitably dividing the river's waters between Texas and New Mexico. However, due to changes in irrigation techniques and other factors, Texas claimed that it was not receiving its fair share of water as stipulated under this compact. The court appointed a Special Master who found that New Mexico had indeed violated terms of the Compact by allowing excessive pumping of groundwater near the river, thus reducing flow downstream into Texas. In its decision, the Supreme Court upheld these findings and ordered New Mexico to ensure delivery of appropriate amounts of water across state lines according to provisions set forth in their original agreement.

In the dissenting opinion for Texas v. New Mexico, 1979, Justice Harry Blackmun argued that the Court should not have taken original jurisdiction over this case. He believed it was inappropriate to resolve a dispute between states about water rights through an original action in the Supreme Court rather than allowing lower courts or agencies with more expertise in such matters to handle it first. Furthermore, he disagreed with how the majority interpreted and applied certain provisions of the Pecos River Compact - an agreement governing water use from a river shared by both states - arguing they had misread its terms and intent. Specifically, he felt that under their interpretation, Texas would be unfairly advantaged at New Mexico's expense contrary to what was agreed upon when signing onto this compact. Thus, while acknowledging that equitable apportionment of interstate waters is indeed within Supreme Court’s purview as per Constitution’s Article III Section 2 Clause 1 granting them original jurisdiction over cases involving two or more States; he still maintained his stance against court’s decision on grounds mentioned above.