Officials with the Management Committee of Taihu Lake said the water quality in east area, the crab zone, has not been affected by the blue-green algae invasion.

Despite this, officials are taking no chances. About 500 kilograms of spiral shells, twice the amount of last year, and 10 million silver carp, 25 percent more than last year, have been put into the zone to purify the water.

The silver carp cost four million yuan (US$529,481).

Taihu Lake is divided into eastern and western parts. The west has only sparse water grass and is now suffering from the algae bloom. The east is in the lower reaches and has a rich cover of water grass, which can prevent algae.

Even more water grass has been added to the east, with the aim of achieving 70 percent coverage.

The annual output of Taihu Lake crabs is more than 20,000 tons. About 75 percent of these are sent to Shanghai markets.

The warm weather this year has also helped in the growth of crabs.

The crabs will be available in local markets by late October and for three months thereafter.