NORTH RIVER A sun-drenched anniversary weekend, a cadre of die-hard volunteers and a river running deep with a late winters snowmelt combined last weekend to produce one of the most successful White Water Derbies in recent years. The event marked the 50th anniversary for the derby and the eager crowds served to chase away rumors that the 2007 Hudson River White Water Derby would be the last. By at least one estimate, this years crowd was double that of last year and the number of participants was up as well, creating a buzz of activity in the hamlets of North River and North Creek. Crowds lined the river bank along Route 28 and strolled Main Street in North Creek, ducking into shops or pausing for a cool beverage while listening to acoustic music in front of the North Creek Deli. With temperatures soaring into the 60s and nary a cloud in the sky, Mother Nature did her part to celebrate the momentous anniversary in what has become a sure sign of winters retreat.