Staff outlines hydrilla control strategy and possible October–November drawdown; carp stocking and permit issues remain under review

Watershed Protection and Austin Water briefed the committee on hydrilla, an invasive aquatic plant that forms dense mats and is impeding recreation on Lake Austin. Liz Johnston (Watershed Protection Environmental Officer) said hydrilla persists in large patches—staff reported it covered about 36% of the lake in the most recent survey—and described why hydrilla is difficult to eradicate because of sediment tubers and rapid vertical growth.

Johnston said the city’s preferred long-term management tool is sterile grass carp. Staff have stocked roughly 5,000 sterile grass carp in Lake Austin since 2025; carp are sterilized by vendors, stocked at sizes (about 10–12 inches) that encourage heavy feeding while minimizing predation risk, and can provide multi-year control if stocking rates strike the right ecological balance. Johnston warned that adding too many carp historically led to loss of all aquatic plants in prior years (a crash after aggressive stocking in 2012–2014), so staff are modeling variables to set an appropriate stocking target. Texas Parks and Wildlife surveys (typically spring and fall, with an extra survey in February last year) inform that modeling.

Teresa Lutz (Austin Water) described the drawdown mechanics and partnership with the Lower Colorado River Authority (LCRA): Austin Water would request a drawdown (dependent on stakeholder input and drought status), LCRA would temporarily store water in Lake Travis while Lake Austin levels fall (staff described a target lowering of roughly 10–12 feet and a normal drawdown window of about six weeks in Oct–Nov), and the lake would be refilled with the stored water so that no net water loss occurs. Lutz said permitting would be required for shoreline maintenance work and highlighted a cost-reimbursement framework to compensate LCRA for lost hydro generation: a base component estimated at $7,000 and a contingency component for extreme market events of up to $68,000—together a possible reimbursement of up to $75,000 in extraordinary conditions.

During Q&A, Council Member Duchin pressed staff on stakeholder appetite for a drawdown, whether drawdowns help hydrilla long term (staff said not reliably), safety risks (staff said anecdotal entanglement reports exist and Lake Patrol has not raised specific safety alarms but constrained access in areas such as Bull Creek is a concern), alternative controls (limited appetite for herbicide among stakeholders; harvesting and bottom-barrier approaches discussed), and the lack of current methodology to quantify economic impacts on tourism or private dock access. Staff said they expect to continue negotiations with LCRA on a letter agreement and hope to make a decision about a drawdown within a month, then communicate to stakeholders so permitting and maintenance planning can proceed if approved.