Lake Arhuaycocha, Glacial lake in Ancash department, Peru.

Lake Arhuaycocha is a glacial lake in the Huascarán National Park, Huaylas Province, Ancash, about 30 km northeast of Caraz. It lies at roughly 4,500 m above sea level, measures 1,107 m long and 400 m wide, and reaches a depth of about 99.4 m. It sits at the foot of the Arhuay glacier tongue descending from Pucahirca Sur (6,039 m) and Rinrihirca (5,888 m).

The lake formed from the melting of the Arhuay glacier descending from Pucahirca Sur and Rinrijirca peaks. This glacial process continues to shape the water's characteristics and the surrounding landscape.

The name Arhuaycocha joins Quechua arway, the lake's own quebrada, with qucha, "lake"; the lake lies in the Santa Cruz District of Huaylas Province. Its shore sits about 100 m below the cauce of the Quebrada Arhuaycocha, on the western flank of the Cordillera Blanca inside Huascarán National Park.

Reaching the site requires driving on a gravel road from Caraz to Cashapampay, then continuing on foot. The hiking section takes several hours and demands proper mountain gear and physical preparation.

Arhuaycocha lies about 100 m below the stream bed of the quebrada of the same name, and its basin records a mean annual temperature of 3.8 °C with roughly 1,250 mm of precipitation. The lake is 1,107 m long and 400 m wide, with a maximum depth of about 99.4 m.