Kansas v. Colorado is a longstanding litigation before the Supreme Court of the United States between two states of the United States, Kansas and Colorado. The Court has rendered numerous opinions in this case:
When two states have a controversy between each other, the case is filed for original jurisdiction with the United States Supreme Court. This is one of the very limited circumstances where the court acts with original jurisdiction, i.e., as a trial court. In all other cases the court acts as the highest level appellate court in the United States.
The issue in the case in 1902 (185 U.S. 125) was whether Colorado, as is claimed by Kansas, is taking too much of the water of the Arkansas River, making the land along the river in Kansas much less valuable due to reduced water flow. The court chose to delay making a decision until all of the facts were in evidence.
In the 1907 case (206 U.S. 46), the Supreme Court affirmed its authority to settle the dispute between the states, but at the same time dismissed Kansas's petition on other grounds. After examining over 8,000 pages of transcripts that had been produced as a result of the litigation, it found that the "perceptible injury to portions of the Arkansas valley in Kansas" was justified by "the reclamation of large areas in Colorado, transforming thousands of acres into fertile fields." The court explicitly invited Kansas to institute new proceedings if the situation worsened significantly.
In the 1943 decision (320 U.S. 383), the court found:
In 1985, Kansas filed suit against Colorado alleging they had overused their share of water outlined in the Arkansas River Compact. For the next 24 years, Kansas spent over $20 million and 250 days in trial to convince the US Supreme Court that Colorado violated the Arkansas River Compact. The courts found that Colorado had indeed depleted flows to Kansas through their development of groundwater pumping installed after 1949. In April 2005, Kansas was awarded $34 million in damages and $1 million in legal costs. Then in March 2009, the final document was issued, requiring the use of a hydrologic-institutional model to bring Colorado to compliance.
In the 1995 case (514 U.S. 673), the court stated