Canada's Mackenzie River basin -- among the world's most important major ecosystems -- is poorly studied, inadequately monitored, and at serious risk due to climate change and resource exploitation, a panel of international scientists warn. Largest single threat to the Basin: a potential breach in the tailings ponds at one of the large oil sands sites mining surface bitumen. A breach in winter sending tailings liquid under the ice "would be virtually impossible to remediate or clean-up."