CARIBOU — Under a steady stream of rain Sunday morning at the Lower Lyndon Street Boat Launch, more than a dozen kayakers and canoeists set off on a 6.2-mile jaunt down the furious Aroostook River. In its sixth year, the Aroostook River Spring Runoff Canoe and Kayak Race is designed to encourage locals to use the river, an asset Caribou is working to reclaim from the industrial facilities that once dominated its banks and kept residents away. On…