Does "It's been decades" mean "The Colorado river has been decades in dusty smear (since it has reached the sea)"?
Context:
A historic US-Mexico deal will see 130 billion litres of water infuse the river's parched delta, leaving an explosion of life in its wakeFROM above it looks like a meandering yellow scar. On either side lie lush green polygons – the irrigated fields of the Mexicali valley just south of the US border, where tomatoes, cucumbers and onions grow in what should be a desert. The dusty smear running in between used to be the Colorado river.
It's been decades since it has reached the sea.
MOre:
http://www.newscientist.com/article/mg22129602.800-huge-water-pulse-to-bring-colorado-river-back-from-dead.html