The pristine environment around Lake Baikal in Siberia, the world’s deepest freshwater lake, is endangered by a joint Russian-Chinese plan to build an oil pipeline through the region, Greenpeace warned yesterday. A month ago, Russian and Chinese oil companies signed a 25-year deal to pump 30 million tons of Russian crude oil to China every year, along a 1,500-mile-long route. Lake Baikal, which reaches a depth of more than a mile and contains one-fifth of the world’s freshwater reserves, was declared a World Heritage Site in 1996 by the U.N.’s cultural agency, UNESCO; Greenpeace is now urging UNESCO to declare the site endangered. The environmental group has previously called on the Russian government to close down a number of environmentally hazardous factories along the lake’s shores.