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Carlsbad outlines multi‑pronged plan after draining Pecos River to fight invasive aquatic bloom
Summary
City staff briefed the council on the Pecos River response: the river was drained, contractors are removing desiccated vegetation, the city plans phased refilling starting May 1, up to eight herbicide applications, and renewed use of sterile triploid carp; staff said experts disagree but the combined approach aims to manage regrowth.
City staff on April 20 gave a detailed briefing on ongoing efforts to control an invasive aquatic bloom in the Pecos River, describing a combination of mechanical removal, phased refilling and targeted herbicide applications.
Ms. Austin said the city contracted an environmental engineering firm and a biologist, posted both reports online, and has a contractor working in exposed riverbed areas to scoop desiccated vegetation. She said the city drained parts of the river and will begin refilling on May 1 with gradual gate closures to control water levels.
As the river is refilled, Ms. Austin said the city will use a contractor (Lehi Bayou) to apply an herbicide on a monthly cycle — staff said the current contract envisions up to eight applications with monthly reevaluation — and will reintroduce sterile triploid carp to target remaining vegetation in channels. Ms. Austin acknowledged that experts do not fully agree on the optimal approach but said draining the river and mechanical removal have shown promising results.
Councilors raised questions about long‑term maintenance, the herbicide's safety for future river users, and whether repeated drain‑and‑treat cycles might be necessary. Staff said the herbicide chosen is a phosphorus‑binding agent and that consultant observations show roots appear dead in scraped areas, though seeds or channelized water could allow regrowth. The city plans regular monitoring and weekly or monthly reassessment as part of its adaptive approach.
