For more than 30 years, the 1,000-mile Yukon Quest International Sled Dog race, which begins Saturday, has followed the Yukon River between Whitehorse, Canada, and Fairbanks, Alaska.A little open water along the Yukon Quest trail is nothing new, but in recent years, long unfrozen stretches of the Yukon River have shaken even the toughest mushers.Last year, musher Hank DeBruin of Ontario had stopped along the Yukon River to rest his dog team in the middle of the night, when the ice started to break up.