By Nestle J. Frobish

Visitors to the Sacramento-San Joaquin Delta are doing double takes lately as they encounter some newly introduced “biological controls” to keep a fast-spreading waterweed from damaging boat propellers and choking off waterways.

Working with state water officials, UC Davis scientists last month released a herd or “bloat” of hippopotamuses from Botswana to chow down on vast mats of water hyacinth that also threaten to clog the intake to the California Aqueduct near Stockton.

Elsewhere in the Delta, the researchers also planted hyacinth-loving manatees imported from Florida and giant guinea pig-like rodents from Brazil called capybaras.

The menagerie of radio-tagged herbivores is part of a yearlong experiment in more natural and, some say, more effective, controls for curbing the menacing growth of non-native aquatic weeds in the Delta.

Enlisting hippos in the biowarfare is the brainchild of Robert Broussard, a professor with the UC Davis Center for Watershed Sciences who has long touted biological controls as a cost-effective way to keep the growth of hyacinth in check.

“What better way to fight an alien species than by introducing still more alien species?” Broussard said.

State and local agencies have poured millions of dollars into chemically and mechanically clearing Delta waterways of the hyacinth, a floating ornamental plant, and the submerged Brazilian Waterweed. But this year the combination of severe drought and slower-flowing, nutrient-laden water has created a perfect storm for waterweed growth. There is no known way to eradicate the weeds.

In some areas the invasive plants have grown so dense that they have threatened not only boat safety and the Delta’s ecological balance but also cargo ship traffic and the state’s water supply.

“Hippos were the furthest things from our minds when we asked UC Davis to find alternative solutions,” said Terry Drinkwater, spokesman for the California Department of Water Resources. “But, I must admit, when it comes to water hyacinth, these river horses are as hungry as, well, horses.”

In their native African habitat, hippos mainly eat aquatic plants, including hyacinth, which they devour at a rate of 200 to 300 pounds a day. The mammal’s affinity for the plant inspired the character “Hyacinth Hippo,” the prima ballerina from the “Dance of the Hours” sequence of Disney’s Fantasia.

“We believe the rate of consumption will be even higher in the Delta with Brazilian waterweed spicing up the mix,” said Broussard, adding that he routinely blends the weed into his own diet of mainly Cajun cuisine.

Officials are taking special measures to keep onlookers at bay because hippos are highly territorial and would likely attack people who encroach on their turf.

The Coast Guard has volunteered a crew to shepherd the bloat of hippos currently grazing in the Clifton Court Forebay, a reservoir that serves as the intake for California Aqueduct diversions to Southern California. Working from jet skis, the crew has been herding the hippos between the forebay and the Stockton Deep Water Ship Channel, where boating and shipping has been stymied by floating mats of hyacinth.

Coast Guard Lieutenant Commander Quinton McHale called the effort in the Delta a “war on weed” and said the public safety interest is no different from law enforcement’s effort to combat marijuana growing along California’s north coast.

“You might as well call the Delta the ‘Emerald Triangle,’” McHale said in a recent interview aboard his patrol board, PT-73.

Stockton Mayor Anthony Silva said he plans to promote the hippos as another tourist attraction for the destination city.

“I’m just trying to think of everything,” Silva said. “You just know darn well there’s got to be a way we can make money off those big bad boys. Hippos in Stockton is a wacky idea, so we’re calling them ‘Weed Whackers’. Get it?”

Researchers will be comparing the hippos with the more gentle manatees and the web-footed capybaras on feasibility, cost and effectiveness in the waterweed control experiment.

Follow-up work will include a special genetic breeding program to create more voracious aquatic herbivores. “If this doesn’t work, we will be considering barriers in the Delta to limit the spread of waterweeds,” said Cornelius Biemond, deputy director of water supply at the Department of Water Resources.

Jake Lunge, director of the Center for Watershed Sciences, said that adding these “four-legged locusts” to the state’s arsenal of pesticide spraying boats and mechanical waterweed harvesters will likely boost the state’s water supply during this fourth year of severe drought.

“Grazing these vast mats of hyacinth will reduce evapotranspiration and save a lot of water,” said Lunge, a civil professor of ornamental engineering.

“This could help keep California from running out of water by the end of the year.”



Nestle J. Frobish, former chairman of the Worldwide Fair Play for Frogs Committee, is curator of the UC Davis Center for Watershed Sciences.

Further reading

Andersen, T. “Water hyacinth thrives in drought-stricken Delta.” Bay Nature. Dec. 22, 2014

Breitler, A. “Stockton mayor floats an idea: Bring in manatees.” The Record (Stockton). Nov. 8, 2014

Breitler, A. “Port of Stockton: Vessel stopped by tangled mats of hyacinth,” The Record (Stockton). Oct. 28, 2014

Fitzgerald, M. “Hyacinth? Think giant amphibious hamsters.” The Record (Stockton). Nov. 3, 2013

Hippopotamus Stew. Cooks.com

Jackson, W.T. and Paterson, A.M. (1977), “The Sacramento-San Joaquin Delta – The evolution and implementation of water policy – an historical perspective.” Contribution No. 163. California Water Resources Center, UC Davis

Miller, G. “The crazy, ingenious plan to bring hippopotamus ranching to America.” Wired. Dec. 20, 2013