In the 1970s, an ephemeral crater lake appeared in the crater after wet seasons; another lake formed in 2016 after the crater floor was covered by the ongoing eruptions with impermeable material. Acid springs occur in the crater, and their water is capable of corroding silicon after a few hours' exposure. Lake Piscococha is located on the volcano's western foot and during December-April receives meltwater from its slopes, while the Para River and Sacuaya River flow past its eastern and southern slopes, respectively. Other rivers on the slopes of Ubinas are the Quebrada Infiernillo on the southeastern, Volcanmayo River on the southern and Quebrada Postcone on the southwestern flank. The Sacuaya River becomes the Ubinas River and after confluence with the Para ends in the Tambo River which eventually flows into the Pacific Ocean; the Ubinas River valley is densely inhabited.