Environment
4:43 pm
Mon January 3, 2011

Lake Austin and the Hydrilla Plant

Lake Austin is getting lower.  The Lower Colorado River Authority is drawing down the lake's level so that City of Austin crews can do battle with hydrilla, an invasive water plant that clogs the lake. 

"It grows and creates very dense mats when it grows up from the bottom of the lake.  Most plants, when they reach the surface just stay there and stop growing.  But hydrilla, when it gets up to the surface, continues to grow," said Mary Gilroy, an environmental scientist with the city's Watershed Protection Department.

The main concern is that the hydrilla can form mats that clog boat propellers and endanger swimmers, who could become entangled in the plant.  It will take a while for Lake Austin to drop the needed 12 feet to help kill off at least some of the plants.  The city uses Asian grass carp to eat some of the plant away, but it also relies on lower water levels to cause hydrilla to dry out and die.

"When the water level drops and exposes the plant to air, then that top growth will just dehydrate and dry up.  Now, because hydrilla is so thick, it is helpful for people to go out and rake the material up and try and pull it up on shore," Gilroy told KUT News.

Gilroy says even when the top layer of hydrilla is pulled off, there's plenty of healthy plant below the water's surface that can grow again.  The lake will be drawn down three to six inches at a time until the level has dropped 12 feet.  LCRA crews are supposed to restore the lake to normal levels around February 13.