Kansas v. Colorado

Kansas (plaintiff) and Colorado (defendant) were parties to the Congressionally approved Arkansas River Compact, dividing the waters and benefits of a shared federal reservoir. After the Supreme Court let Kansas sue over Colorado's alleged violations, a special master found Colorado's post-Compact increase in groundwater pumping had materially depleted the river in violation of the Compact and recommended unliquidated damages plus prejudgment interest running from 1969. Colorado objected that prejudgment interest shouldn't apply to unliquidated damages at all, that the interest rate (based on individual rather than state borrowing rates) was too high, and that any interest should start no earlier than 1985, when Kansas actually filed suit; Kansas countered that interest should run all the way back to 1950, the date of the first violation. The United States intervened given its own interest in Colorado flood-control projects and urged that both states' objections be overruled.