Meet the underwater gardeners that scrub Imperial County’s water canals

Photo: IID Operations Coordinator Pablo Cortez, left, holds an adult grass carp while Tony Perez, a colleague, collects the fish’s eggs during spawning season at the Imperial Irrigation District’s grass carp hatchery in El Centro in Imperial County on May 7, 2024.

As summer approaches, the Imperial Irrigation District is gearing up for another battle with the weeds that infest its canals.

To do that, the regional water agency is calling in reinforcements: a small army of plant-munching fish.

Water weeds are a common problem for many irrigation districts, since shallow canals and clear water create a welcoming environment for aquatic plant life. The weeds regularly clog up the system of gates and channels that ferry water to farms throughout Imperial County.

To fight the spread, the Imperial Irrigation District, or IID, unleashes thousands of grass carp, a river fish native to North Vietnam and other parts of Asia. The stocky carp have a massive appetite for aquatic plants and can eat more than double their body weight in less than a day.

“We put them in the canals, and they basically become IID workers,” said Pablo Cortez, who leads the district’s grass carp hatchery program. “It’s very effective.”

Wild grass carp are invasive species considered a public enemy by state authorities. The species can decimate native ecosystems if left unchecked. The California Department of Fish and Wildlife has made it illegal to import them in most cases and issued kill orders in certain counties.

But IID uses its own genetically-altered grass carp, which the district raises at a hatchery in El Centro. Hatchery workers place each batch of carp eggs under immense pressure during the fertilization process, creating young fish that have extra genetic material and are effectively unable to reproduce.

This method of sterilizing grass carp and using them to control aquatic weeds sounds futuristic, but it’s been employed widely in […]

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