The ability of several of Colorado's prime ski areas to respond to winter drought is threatened by acidic runoff from abandoned mines, according to researchers at the University of Colorado at Boulder and the Northwest Colorado Council of Governments. Contamination known as acid-rock drainage enters waterways, such as Summit County's Snake River, that are used for making artificial snow. When the snow melts, the water can run into streams not previously polluted, further spreading the contamination, said the research team.