In an ongoing effort to gain control in Lake Austin over the rapid spread of a non-native exotic weed, hydrilla, City of Austin officials released 9,000 sterile Asian grass carp off the Mary Quinlan Park dock on May 2.

According to the City of Austin's Watershed Protection Department website, hydrilla can grow up to one inch per day and fish, such as carp, eat the hydrilla as a biological method to control the issue.

"We had five years, from 2005 to 2010, of good control," said Mary Gilroy, an Environmental Scientist with the City of Austin's Watershed Protection and Development Review Department. Gilroy said that in 2011, when the drought caused water levels to drop in Lake Travis which feeds into Lake Austin, the Lake Austin water heated up and produced the warm type of environment which hydrilla thrive on.

Gilroy's office, along with the Texas Parks and Wildlife Department, the Lower Colorado River Authority and the citizen group, Friends of Lake Austin, participated in a management plan which periodically stocked the lakes with the carp to keep the hydrilla in check, covering less than 80 acres of Lake Austin.

About 17,000 fish were stocked in Lake Austin in 2012, for a stocking rate of 50 fish per acre of hydrilla, Gilroy said. However, by February of 2013, the hydrilla level in the lake had increased, prompting this month's carp release. The May 2 release is expected to bring the carp stocking rate up by 10 percent, to 55.5 fish per acre of hydrilla.

"We're hoping that this 10 percent increase will be enough to gain control over the hydrilla," Gilroy said. "But [the hydrilla are] living organisms and we can't predict the outcome."

Gilroy said that the hydrilla currently covers 600 acres of Lake Austin.