The State of Kansas (plaintiff) and the State of Colorado (defendant) entered into the Arkansas River Compact (Compact), which was approved by Congress in 1949. The Compact was designed to equitably divide and apportion the waters and the benefits from the construction and operation of the federal John Martin Reservoir. In 1986, the United States Supreme Court granted Kansas leave to file a complaint alleging violations of the Compact by Colorado. Special Master Arthur L. Littleworth recommended that two of the claims should be denied, but that the Court should find Colorado’s post-Compact increases in groundwater well-pumping to have materially depleted the waters in violation of the Compact. In a second report, the special master recommended damages. Colorado objected because Kansas had inexcusably delayed filing its complaint. The Court overruled the objection because the nature and extent of Colorado’s wrongdoing had not been immediately clear. In a third report, the special master recommended that Colorado should pay unliquidated money damages with prejudgment interest accrued from 1969 to the date of judgment. Colorado objected that prejudgment interest should not be awarded on unliquidated damages, that the interest rate was excessive because it was based on what was available to individuals and not to states, and that any interest should only accrue from 1985, the time the complaint was filed, rather than 1969. Kansas objected that prejudgment interest should be paid from 1950, the date of the first violation of the Compact, rather than from 1969, the date on which the special master found that Colorado knew or should have known it was violating the Compact. The United States intervened because of its interest in operating flood-control projects in Colorado and argued that both states’ objections should be overruled.