In the 1970s a minor eruption from Mount Ruapehu spilled some of the contents from the Ruapehu Crater Lake (the same root cause of the Tangiwai disaster). This toxic water entered the Whanganui River and had the effect of killing much of the fish life downstream. In the aftermath of the poisoning, eels as large as and trout as large as were washed up dead along the banks of the river. The tributary Whakapapa River had fish losses due to a lahar from Ruapehu in April 1975. Possibly this had effects downstream.