California’s Oroville dam crisis demonstrates the major risk of hydroelectric power generation: massive flooding after structural collapse. Using official data from the International Energy Agency and OECD, the New Scientist calculates a global death scale for various energy sources. The range shows immediate or subsequent deaths for every 10 terrawatt-hours (TWh) of power generated around the world:

Coal – 2.8 to 32.7 deaths per 10 billion KWh 

Hydroelectric – 1.0-1.6 deaths per 10 billion KWh

Natural gas – 0.3-1.6 deaths per 10 billion KWh

Nuclear – 0.2 to 1.2 deaths per 10 billion KWh 

Even after nuclear disasters like Chernobyl and gas explosions are accounted for, hydroelectric power has still caused more deaths per unit than either. Hydroelectric collapse also threatens the very environment renewable sources are intended to protect: deadly quantities of silt have been displaced in Oroville, leading the California Department of Fish and Wildlife to launch a daring operation to rescue millions of fish (the state has an $8 billion fishing industry). Turns out holding back millions of gallons of water behind walls near a major town and cities isn’t risk free…