What killed tons of fish in European river? Mystery deepens

Volunteers recover dead fish from the water of the German-Polish border river Oder in Lebus, eastern Germanny, Saturday, Aug. 13, 2022. Poland’s environment minister says laboratory tests following a mass dying off of fish detected high levels of salinity but no mercury in waters of Central Europe’s Oder River. (Patrick Pleul/dpa via AP)

What killed tons of fish in European river? Mystery deepens