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Paraguay Dealing with Lethal Algae Bloom in Ypacara Lake

Aquatic plants are thriving off of the nutrients in the water and along the bank. Their ubiquity shows the presence of pollutants in the lake.

Aquatic plants are thriving off of the nutrients in the water and along the bank. Their ubiquity shows the presence of pollutants in the lake.

Paraguay Dealing with Lethal Algae Bloom in Ypacaraí Lake


The singer Julio Iglesias immortalized Paraguay’s Ypacaraí Lake (“Holy Lake” in the local Guarani language) to Latin music lovers with the song “Memories of Ypacaraí.” But now, Paraguayans are worried that their favorite resort lake could indeed become a memory as it becomes increasingly choked with contamination and toxic algae.

One of the proposed solutions to the problem is to conduct environmental dredging of the lake – but leaders in Paraguay are still split about whether this is the most effective method to stop the bacteria.

The Ypacaraí is just 30 miles east of Paraguay’s capital, Asuncion, and plays in important part in the region’s life – both work and recreational. The 14-mile-long, three-mile-wide lake is second largest body of water in the landlocked nation, and it has long been favored as a summer destination, attracting legions of Paraguayans and foreigners to its sandy beaches and the charming towns that surround them. The lake is shallow – mostly less than about 10-feet deep -- but is plied by fishing boats, sailboats, ski boats and jet skis.

In addition to being a recreation facility, the Ypacaraí’s waters are a source of potable and irrigation water. It has 20 inflowing tributaries, and is drained by one river, the Rio Salado, which drains the lake and joins the Paraguay River at about 15 miles downstream. An extensive area of wetlands with luxuriant growth of emergent and submerged plants near the lake’s outlet maintains the lake water level within a narrow range of fluctuation.

But the much-loved lake’s health has been declining in recent decades. Much of Ypacaraí’s catchment basin is still rural, made up of cropland and pastures. Deforestation has caused serious siltation problems, pouring loose dirt and other nutrients into the once-clear lake and reducing its depth, which in turn has increased its temperature. And the Ypacaraí’s shores have become increasingly urbanized. Local infrastructure has not caught up with the growth, so industrial waste flows into the lake, and often when it rains, local sewage systems dump there too.

All of this has resulted in a perfect environment for algae to flourish. Cyanobacteria, or blue-green algae, can be found in almost any body of water, but in the Ypacaraí it is the number-one resident. It thrives off of nitrates and other nutrients, and in the right conditions can convert a formerly clear waterway into a dense forest of verdant slime. Some cyanobacteria produce neurotoxins that can be very dangerous to humans, animals and marine life, and recent research has linked those poisons to Lou Gehrig’s disease (amyotrophic lateral sclerosis).

The algae blooms in Ypacaraí are periodic – sometimes they subside, thanks to the weather, season or natural life cycle of the algae – but when they are at their most dense, the lake becomes so poisonous that people are not allowed to swim in it. This in turn harms the region’s economy, which has evolved to be dependent on tourism.

Algae blooms are not a new problem, according to Sofía Vera, who is in charge of monitoring and managing the lake for Paraguay’s environmental protection agency, Secretaria de Ambiente (SEAM). She has been working at the agency since 1982, which has been trying to address the issue for at least that long, but to no avail.

In recent months the problem grew to be so severe that the mayors of four of the towns that border the lake – San Bernadino, Ypacaraí, Itauguá and Areguá – asked experts to assess the situation and come up with solutions.

Marinus Pool of Holland and Alberto Boccato of Italy, both of whom are consultants with Beta Studios in Italy, visited Lake Ypacaraí in October to investigate the problem, and are now compiling a report with recommendations. Top among those recommendations is to conduct environmental dredging to alleviate it – at least short term – from the algae infestation. The dredging would also help oxygenate the water, which is oxygen-sparse because of the algae. The report will also include suggestions for the longer-term restoration of the Ypacaraí, like restoring the nearby wetlands and planting aquatic vegetation in the lake, both of which can help subdue the algae and bring the waterway back to a measure of health.

“We were in Paraguay the other week to analyze the situation, and we’re proposing a master plan,” said Boccato.

The master plan focuses on several stages of improving the Ypacarai’s health, including improving the sewage system and stopping the flow of industrial waste into the lake. It also calls for the restoration of the wetlands, measures to stop sediments flowing into the lake, and educating the population who lives on its shores about how to care for it. They also call for the re-routing of the most contaminated tributaries of the lake.

Since all of those measures are long-term (up to 10 years), Boccato and Pool are also proposing short-term solutions, including dredging the Ypacarai. The objective of dredging would be the removal of the organic cap on the bottom of the lake, which causes turbidity and lack of oxygen.

“The problem of the high-cost of transport and disposal of the dredged material can be solved by adopting a specific dredging technique, which consists of working without touching much of the organic layer,” Boccato told the IDR. “It will not be removed from the lake, but instead will be buried about two meters under the sand. In this way, you can prevent direct contact between the black layer and the water.”

But leaders of the environmental agency said they aren’t so sure – at least not yet. Vera said that the government is conducting studies to understand better the topography of the lake, and considering whether dredging is really the right answer for them. Dredging done wrong could do more damage than it fixes, she said.

The environmental agency’s technicians have said this method of dredging would be “much too drastic,” killing not just the algae but also the plants that are working to rehabilitate the lake. And rerouting the tributary would stop some inflow of algae, but it would also stop inflow of rainwater that nourishes the lake, she said.

After they complete their bathymetric studies of the lake, the government will consider a more limited form of dredging, making some parts of the lake deeper and dredging out areas where the algae is so thick that light doesn’t reach the bottom, she said.

Everyone agrees that dredging must be just one of many measures taken to restore the Ypacaraí to health.
The lake reached its highest level of algae contamination in mid-September, but then some heavy rains and other factors reversed the bacterial growth and now the Ypacaraí is back to its normal level of infestation.

Nonetheless, the mayor of nearby town Areguá and his colleagues in other cities on the lake called upon Paraguay’s government to take quick action on the issue, before it returns. Osvaldo Leiva and the other mayors met in late October in attempt to address the situation.
“We think the recommendation of the Europeans who visited the country a few weeks ago, of dredging the Ypacarai to reduce the level of contamination, must be considered urgently,” Leiva told the newspaper Ultima Hora.

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