By 2020, the Spokane River will look more like a blue-ribbon trout stream, Washington state officials predicted Friday as they unveiled a final plan to reduce the river’s phosphorus load by 90 percent within a decade. Anglers will slip on fewer slimy, algae-coated rocks along the shore, they said. More oxygen will be available for fish and other aquatic creatures in the river, and the reservoir behind Long Lake Dam will be transformed, with oxygenated water extending another 50 feet deep, and fewer outbreaks of toxic algae blooms.