Threats due to drought and overuse continue to threaten water availability in the Rio Grande River Basin in Southern Colorado and all along its entire 1,900-mile-long course. That’s according to a new study by the World Wildlife Fund, Sustainable Waters and various universities. … Researchers say 52 percent of the basin’s water used directly for human activities isn’t replenishable from renewable sources like snow melt. The study points to irrigated agriculture, which comprises about 87 percent of the use in the entire river basin, combined with lower snowfall, as the primary causes of depletion.