At 2000 m above sea level, the river changes its course to a westerly direction, squeezing through the narrow gorge of Cañon del Pato ("duck's canyon") before it finally breaks through the coastal ridges.

Upstream of the hydroelectric power plant at Huallanca, the Santa River watershed covers an area of 4,900 km2, downstream another 7,300 km2.

Beginning in 1702 when a glaciological flood is first recorded, the valley has repeatedly suffered deaths and destruction.

In 1962 and 1970, a massive avalanche of ice and rocks tumbled down from the western slopes of Huascarán and then roared down the river valley.

Devastating landslides like these will always threaten the region, when falling glacial ice triggers sudden drainages of ice-dammed lakes in the mountainous region and liquid mud, blocks of ice and large rock boulders crash down the narrow valleys.