Abstract: The Katun River originates in the steppe of the Altai Mountains in Siberia. One of the major headwaters of the Ob River, the Katun is considered central to the culture of the indigenous Altaians. The Katun Valley contains large numbers of important cultural sites, dating from the Neolithic and representing some of the earliest human settlement in Russia. Modern-day Altaians still observe traditional ceremonies honoring the river and springs throughout the watershed and utilize traditional ecological knowledge in their management of the land and water resources. Russian and international scientists have identified the Altai Mountains as a region of high plant diversity and endemism, and as important habitat for endangered species such as the snow leopard. The Katun River itself contains species of threatened and endangered fishes, and its headwaters are part of the unusual Mongolian ichthyofaunal province that is characterized by high levels of endemism. The same regions are considered by the Altaian people to be special or sacred and are recognized by Western scientists as having great value for conservation. During the era of perestroika, a hydroelectric dam was to be built on the Katun. The large dam, a vestige of the earlier Soviet plan for the Project of the Century, would have devastated significant agricultural, ecological, recreational, and cultural resources. The indigenous Altaian people would have lost much of their sacred and cultural landscape. The Katun dam project united indigenous people, well-known Siberian writers, and scientists in protest, which became so heated that it engaged the international community, with lasting effects on Russian society. The magnitude of the protest illustrates the importance of the Altai Mountain region to all of Russia. The active participation of indigenous Altaians reflected their traditional willingness to take action against political decisions that negatively impacted the environmental, cultural, and religious values of their homeland. Their involvement also reflected the new wave of awareness under perestroika that underscored a greater respect and autonomy for indigenous peoples in Russia.