An emergency alert to the fishing industry in the Zhoushan Island region of Zhejiang province has been issued warning that crabs, clams and other shellfish caught in the area could be harmful to the health of consumers, Pan Yue of the State Environmental Protection Agency told the China News Service.

The red tide has spread over an area 200 kilometer (120 mile) long and 100 kilometer wide.

Worst hit was a 10,000 square kilometer area around Taizhou Yushan Islands just outside the mouth of the Yangtze river where scientists determined that the algae bloom was toxic, the report said.

The dangerous tide, first spotted in early May, was likely to expand before it gets smaller, Pan said.

A "red tide" is a densely populated algae bloom that breeds in abundance and suffocates fish by sapping the water of oxygen while also producing toxins that can paralyze fish and contaminate seafood.

The algae mainly feasts on urban pollution, industrial discharges, farming wastes and fertilizer run-off that are rich in nitrogen and phosphorus and which flow into coastal waters from rivers and streams.

China's coastal regions have been ravaged by springtime red tides in recent years, especially in the northern Bohai Sea, the East China Sea and the South China Sea near the mouth of the Pearl River.

TERRA.WIRE