A flood triggered by recent torrential rains poured into Baiyangdian Lake in Hebei province, leading to unhealthy conditions in the water that caused thousands of tons of fish to die of suffocation, the local government said.

It's estimated that about 1 million kilograms of fish were killed in nearby waters over an area as large as 133 hectares in Baoding, in Hebei province, over three days. Economic loses may reach 10 million yuan ($1.6 million), according to the fish farmers.

The official announcement said the floodwaters and currents stirred up fish food and waste in the lake, decreasing oxygen in the water and killing the fish.

But fish farmers believed that pollution is the primary cause.

Wang Xiaocang, who has bred fish in the lake for years, found a stream of dark red sewage flowing into his pond on Aug 12. Hours later, all his fish were dead, Beijing Times reported on Aug. 27.

The farmers believe the pollution came from companies upstream, and they will launch an investigation and may sue some companies.

Compensation will be given to the farmers as soon as possible, the government said.