La Paz - Authorities in the eastern Bolivian province of Santa Cruz declared an alert following the death of 6 million fish from the unusually cold weather gripping the country in recent weeks.

The provincial government said the fish died in the Grande, Pirai and Ichilo rivers that run through the tropical region.

This is an "environmental catastrophe" brought on by the lowest temperatures registered in Santa Cruz in nearly half a century, Gov. Ruben Costas told reporters.

He said that environmental personnel who visited the disaster areas found that the three rivers are highly polluted by dead fish, and he warned locals not to use those waters.

He said that his administration will send equipment to the towns on the banks of those rivers to supply the inhabitants with drinking water and prevent a public health disaster.

Costas also announced that in the coming days he will order a closed season for fishing in the tributaries and also for hunting, with the goal of progressively "repopulating" the fauna of the region.

The cold wave that gripped the Southern Cone of South America last month caused a severe drop in temperatures in southern and eastern Bolivia, even falling below 0 C (32 F) in areas where the thermometer is usually above 20 C (68 F).

Bolivia's weather service has announced that a new cold front will enter the southern and eastern parts of the country this week.