photo by Carp Anglers Group

More than 2,000 grass carp were released into Lake Austin Thursday to help control the spread of the hydrilla weed.

The spread of the non-native hydrilla has covered no more than 80 acres in the waters of Lake Austin for the last four years, but since this September, its growth has surged to four times as much.

That led to the release the Asian grass carp. The carp have been the city's best weapon over the years for combating the spread of hydrilla.

The fish species hails from the same region as the weed, however the city said that the carp don't pose an environmental threat like the hyrdilla does.

"These fish are what are called triploid. That means they have an extra set of chromosomes, so they cannot breed. They're sterile, basically; and so we can stock fish in the lake, but they will never establish a breeding population," City of Austin environmental scientist Mary Gilroy said.

Before the end of the year, the city plans to stock another 2,200 fish, bringing the estimated total of fish in the lake to 7,400.