Invasion of the killer blooms

Rampant water hyacinths are choking the Presa Allende

If you were charged to engineer the perfect invasive plant, you could hardly do better than the water hyacinth (lirio acuático, in Spanish), which has been nicknamed by some as “the weed from hell” or “the terror of Bengal,” and is now spreading explosively throughout the large water reservoir behind the Presa Allende.

Water hyacinth’s beguiling beauty at first sight—its profuse, lavender flowers and glossy green leaves—conceals an insidious, below-the-water propagation habit that allows it to double in size in as little as one to two weeks, while producing thousands of seeds that remain viable for as long as 20 years.

Roots of the problem: Hyacinths develop into thick mats

Hollow spaces in parts of the plant keep it afloat, while an overall water content of 90 to 95 percent functions as ballast. The root systems then intertwine and fuse hyacinth colonies into dense floating mats all but impenetrable by small boats and kayaks, that can also block sunlight and stifle other plant and fish life underneath.

Additionally, the fleshy, spoon-like leaves can catch the wind and send the mats or islands of hyacinths drifting across the water. In parts of the Presa Allende, hyacinths colonies have proliferated as far as the eye can see in only a couple of years and have bunched up by the the presa (“dam”) itself.

The Presa Allende, a significant engineering project, was inaugurated in 1969 and meant to prevent periodic flooding by the Laja River, while providing irrigation for farming and secondarily, create a recreational area. The surface capacity is about 23 square kilometers, though that, and the depth of water, fluctuate widely depending on rainfall.

Creation of the Presa Allende forced small waterfront towns, such as La Pantoja, to move to higher ground. Since then, residents have relied on brickmaking and fishing for carp and mojarra for their livelihood.

During dry weather, a church steeple and other structures from the submerged town poke out of the water. In shallower areas the Presa has become a refuge for white pelicans, herons and other aquatic birds.

A perfect storm?

In November 2020, following a poor rainy season, the Presa Allende’s reservoir was at 17 percent capacity, the lowest level in several years. A year later it was overflowing.

Although there is no conclusive explanation for the recent plague of water hyacinths, one reason could be the sharp fluctuation in water levels, according to April Gaydos, an expat resident of San Miguel for 12 years, and head of the local chapter of Audubon de Mexico, an environmental group that has been lobbying local authorities to take action regarding the Presa’s predicament.

Her hypothesis is that the 2020 drought may have exposed viable water hyacinth seeds lying at the bottom of the Presa, for perhaps decades, to the sun and air, and which then germinated when the rains returned and the reservoir filled beyond capacity a year later.

Also, years of discharges of raw sewage by municipalities upstream from from the Presa, including San Miguel whose sole water treatment facility is risibly inadequate, and fertilizer runoff from farms, combined to create a so-called “nutrient-rich” soup that encouraged the lightning spread of the hyacinths.

Turning lemons into lemonade

Whatever the cause, local government and Mayor Mauricio Trejo appear to be fully cognizant of the problem, though its remediation plans have been more fits-and-starts than a concerted effort.

Chugging away in an ocean of hyacinths.

It has hired a machine, resembling a floating combine, to scoop up the hyacinths, which are then collected by a backhoe and piled by the shore or carted away in dump trucks.

It would be an encouraging sight if the lonely machine weren’t chugging away amid a green ocean of water hyacinths that continues to spread. Equally hopeless were scenes earlier this year of temporary workers, in wading boots, flinging the waterlogged and very heavy hyacinths onto the shore with pitchforks.

And of course, after their removal to shore, the question remains what to do with the mountains of dead plants, which are tainted by arsenic and other contaminants. So far, the only reuse undertaken by the municipal government is to use some of the debris as compost or mulching in tree-planting projects throughout the city.

Remains of yesterday: Abandoned waterfront cantina.

During a half-hour, May 2022 interview with Atención newspaper, San Miguel Mayor Mauricio Trejo, says he recognizes the seriousness of the problem but his proposals sound more like wishful thinking. He claims the area covered by the plants has been reduced dramatically, but Audubon’s Gaydos suspects his numbers are wildly inflated, and that recent aerial photos show as much as 60 percent of the Presa covered by the hyacinths—and still growing.

Trejo’s proposals aim to turn an environmental crisis into economic opportunity, such as incorporating dried hyacinth debris in the brickmaking process at La Pantoja, or as fuel or composted fertilizer. Or building a new $180 million peso sewage treatment facility for San Miguel. Or hiring more local people to manually remove some of the water hyacinth, a Sisyphean job-creation undertaking if there ever was one.

No work for two months: Fishermen Alberto Valdez (l) and Salvador Cerritos.

Good ideas all, except his lemons-into-lemonade visions are undercut by financial realities. The National Water Commission, which is in charge of all water-related issues, both surface and underground, so far has not come up with any funding, and neither has state government, he said. And water hyacinth remediation, he added, is but one of many, arguably more pressing municipal responsibilities, such as schools, health and roadbuilding.

Yet the economic impact of the problem is immediately clear. By the Presa itself, abandoned small waterfront restaurants, and boat ramps half-covered with live or dead water hyacinths, speak to the real recreational past of the area not too long ago. And so can dozens of local residents who relied on fishing for a living and now can only wait for the mats of hyacinths to recede, or for local government to hire them for the enormous task of removing them. A more ominous reality is that, failing a concerted effort to tackle this crisis, the Presa Allende reservoir itself might cease to exist as living body of water.


12 thoughts on “Invasion of the killer blooms

  1. Sharon

    I live in South Florida and we have similar problem with water lilies. I did a quick google search and found this: “Control is best achieved through killing of the root system by application of herbicide to the leaves above the water. Cutting water lilies under the waterline 2 or 3 times to drown them can actually stimulate growth. Pulling them out by the roots can be impractical.” Just a thought, it might not be practical in Mexico.


    1. Thank you for your comment, Sharon. I have read the same thing, and a number of other ideas for controlling this plant, including bringing in manatees, which apparently like to eat them. This problem just came up here during the past 18 months or so, and they haven’t developed a comprehensive control strategy yet. Using chemical controls, I imagine, could work if they are used very carefully, so as to not create more contamination problems. Thanks again.


  2. Luke Rich

    Good job. The one thing you didn’t emphasize is that the Presa Allende is a Federal project built with Federal money and the primary responsibility for dealing with this or any other issue related to the Presa lies with CONAGUA. They have done nothing. I’m told Lake Chapala has the same problem and nothing being done by the Feds there either.
    It is a real mess which is beyond the capacity of any small city including San Miguel to deal with.


    1. Thank you for your observation Luke, which is well taken. I did mention that the federal agency of all things water, above and below ground, hasn’t done a thing to combat the problem. And certainly developing much less launching a comprehensive program for controlling water hyacinths—including construction of an adequate sewage treatment plant—would cost millions more pesos that the local municipality can afford. Maybe there is no solution and we’ll just have to wait and see what happens when the problem turns into a major crisis. Thanks again.


  3. norm

    The pre Colombian people of Latin America used the water lilies as fertilizer. The plant was cut and raked from the canals and waterways, piled in heaps to break down into compost and then spread on their fields. It was a regular occupation. The process fed millions in central and southern Mexico for a thousand years.
    The water lily is a common symbol in pre Colombian art. Rain and corn are more common but the water lilies are right in there, it was very important to their life style in places that would support open water farming.
    Maybe those pesky flowers could be put to a better use than filling up a landfill.


    1. Norm: You’re a pretty amazing fellow: Where do you such interesting nuggets of information? The municipality is trying to use the dried up water lilies for mulch in a tree-planting program somewhere else in the city. And I imagine the dead water lilies could be run through a shredder and composted, just like the Mayans did. The only catch I see in such a program is that there’s a high level of arsenic and other heavy metals in the water, so someone would have to do some serious research before they introduce water lilies compost into the food chain. Good idea, though. Thanks again. Al


  4. There’s a similar, though lesser problem in Lake Chapala. There some residents volunteer to manually drag the plants out of the water, but as you note, it’s a Sisyphean task. Alas, in Mexico, there are far more pressing concerns than choked lakes and reservoirs. And Mexico’s creaky bureaucracy seems overwhelmed by the simplest of of tasks: issuing taxpayer identification numbers, processing permissions for foreign residents to buy property, and even keeping motorcyclists from consistently running red lights. Asking it to control an invasive plant, however important, just isn’t likely to get done.


    Kim G
    Roma Sur, CDMX
    Where I dread ever needing any kind of remodeling permit.


    1. Thank you for your comment Kim: I’ve heard that Lake Chapala’s problem may be worse. When we visited, about 15 years ago, the lake had receded about 300-400 meters and seemed all but dead, supposedly due to fertilizer runoffs upstream. But I’ve heard it’s recovered. You’re right that in a country with limited resources, it’s a matter of priorities. Or: “poco dinero y demasiada corrupción.”


  5. It’s just a matter of creating a market for water hyacinth, convincing people that it cures male pattern baldness, obesity, insomnia, impotence, failing eyesight, every problem of aging, that is makes the ugly attractive, raises IQs, solves world hunger problems, reduces carbon footprints, and is highly valuable in other, yet-recognized aspects. It could be the new quinoa, the new new moringa, the new kombucha. And that whatever arsenic levels might repose within are actually good, preventing and curing heartworms that people didn’t even know they had.

    You’re a word merchant, and Stew’s a creative. You guys could create something out of this, making San Miguel the Water Hyacinth Capital of the World and yourselves rich. You could become the new Kelloggs.’

    BTW, the new blog design is fab!

    Liked by 1 person

    1. Jen: Forget jurisprudence and try marketing! This idea is pure genius. Octogenarians in town already patronize all sorts of quackery, and water hyacinth treatments—smoothies, teas, colonics, mud baths, to name a few—wouldn’t be that much stranger, and likely cheaper, given the endless supply of raw materials from the presa.
      Glad you like the new design and thanks again for encouraging me to make the move, which wasn’t that traumatic to begin with.


  6. Barbara Eckrote

    Mother Nature has taken over! It happened in Ajijic about ten or twenty years ago and somehow they got rid of them. The lake was infested.


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