RICO — An otter popped up in the once-toxic water. Its appearance last winter — devouring a trout — has ignited hopes around an experiment to transform a scarred, mining wasteland into a naturalistic mountain valley. This re-engineering along headwaters of the Dolores River requires replanting wetlands with native grasses and laying in soil to mimic natural processes — an innovative approach that may be deployed more widely across the water-challenged West, where tens of thousands of toxic mines foul rivers and streams.