Could the dead fish be from the unusual cold weather or drought around the world? Fish are very sensitive to water temperature, so maybe Global Cooling [ie the New Ice Age], is effecting water temps which is killing the fish???

There was a massive fish kill along the Amazon river last summer [So.America's winter] due to extremely cold weather that cooled water temperature to the point that millions of fish died.
"Over 1 million fish and thousands of alligators, turtles, dolphins and other river wildlife are floating dead in numerous Bolivian rivers in the three eastern/southern departments of Santa Cruz, Beni and Tarija. The extreme cold front that hit Bolivia in mid-July caused water temperatures to dip below the minimum temperatures river life can tolerate. As a consequence, rivers, lakes, lagoons and fisheries are brimming with decomposing fish and other creatures."

[link to www.nature.com]

[link to www.boliviabella.com]