The bloody Battle of Yahuarcocha was in 1487. The Cayambis had realized that their forces were not enough to fight the Incas in an open field battle, and according to the Spanish missionary, Bernabe Cobo (17th century- History of the Inca Empire), they retreated to make a great fortress. So, Huayna Capac ordered his men to besiege the fortress and bombard it continuously.

The Cayambis put a great resistance and forced the Incas to retreat due to the large number of deaths. Huayna Capac gathered together a large army and definitively subdued the "rebels".
Finally the Incas got carried all Cayambis of their fortresses toward the shore of the lake and kill them.

A massacre in the Lagoon of Yahuarcocha
When Huayna-Capac finally conquered the tribes, historical documents record that he massacred all the Caranqui men aged 12 and older and threw their bodies into Yahuarcocha lake, whose color turned red from the blood.

Cobo writed that "the Incas ordered their men to cut the enemies' throats mercilesly, because they had hunted them in order to threw their bodies into the lake."