In the case of Montana v. Wyoming (2017), the Supreme Court was asked to resolve a dispute between the two states over water rights from the Tongue River, which flows northward from Wyoming into Montana. The disagreement centered on whether or not Wyoming's increased use of irrigation methods that reduced runoff back into the river violated an interstate compact agreed upon in 1950, which allocated each state certain amounts of water from shared rivers and streams. In its decision, the court sided with Wyoming, ruling that while these new irrigation techniques did reduce return flow to downstream users in Montana, they were within legal limits set by beneficial use requirements under doctrine established by prior appropriation states like both parties involved here. Therefore it concluded that no violation had occurred because such changes are considered improvements rather than enlargements or alterations as defined by this agreement.

The dissenting opinion in the case of Montana v. Wyoming argued that the majority's decision was inconsistent with the Yellowstone River Compact, a congressionally sanctioned agreement between Montana and Wyoming governing water rights to the river. The dissenters believed that this compact should be interpreted as requiring each state to maintain historical consumption levels rather than allowing for increased usage due to technological advancements or efficiency improvements. They contended that by permitting Wyoming to increase its consumption through more efficient irrigation methods, despite reducing return flows downstream, it violated both letter and spirit of compact which aimed at equitable apportionment of waters among signatory states. This interpretation would potentially allow one state to unilaterally alter agreed-upon allocations without any recourse for other parties involved.