Nosara, Nature

Fecal bacteria from septic tanks contaminate the Nosara River and Guiones Beach

Esta publicación también está disponible en: Español
Translator: Arianna Hernández

A new Wildlife Conservation Association (WCA) study revealed that fecal bacteria end up in Guiones Beach and the Nosara River due to septic tanks not working properly on Nosara properties. 

WCA took samples from the Nosara river and two sections of the Guiones Sea during the summer and winter seasons in 2022. The new study is a continuation of the sampling WCA has been carrying out since mid 2020 to monitor fecal bacteria in the district’s waters.

Last October, the team detected large amounts of fecal coliform bacteria -organisms that originate in human and animal intestines- in the Nosara River. These bacteria appeared in much lower amounts at Guiones Beach.

Back then, the scientists argued that the lack of fecal bacteria on the beach could be because coliform bacteria may not tolerate salt water well. They also deemed it plausible that other organisms would be found. As a result, the more recent samples were additionally screened for enterococci -fecal bacteria that survive longer in salt water.

Due to this change in methodology, the researchers went from detecting fecal bacteria in approximately 5% to 19% of the beach samples.  The new study confirmed that, although leakage occurs throughout the year, contaminated water flows more easily to the beaches and the Nosara River during the rainy season.


Research Director and WCA founder Vanessa Bezy explains that during winter, old, full or badly installed septic tanks leak wastewater, which finds its way into the streets. The rain water washes all of the bacteria into the district’s creeks and estuaries, eventually ending up in the ocean. It is a recurring problem each time it starts to rain.

Bezy adds that this study does not allow researchers to determine who is responsible for polluting the district’s rivers and ocean water. Nonetheless, her team did attempt to trace the bacteria’s place of origin by taking multiple samples along the Nosara River, from the river mouth up to its source in Hojancha.

Tourism and urban growth possible causes

According to the results, most of the bacteria are concentrated at the mouth of the river, in the Nosara district. This rules out the organization’s first hypothesis, which suggested that the contamination of the river could come from agricultural activities in the upper part of the river basin.

“All of these results indicate that the pollution we see at the river mouth comes from local sources in Nosara,” the study states. Based on the geographic results, Bezy believes that the septic systems of buildings, both new and old, are among the most polluting activities in the area.

The deputy director of the Tempisque Conservation Area (ACT), Mauricio Méndez, states that it is common to see this type of contamination in communities without planned and orderly urban development.

When there are rivers near the coast, in areas populated by tourism, the underlying causes are generally properties, whether they are residential, hotels or restaurants. In Costa Rica, wastewater management is terrible across the board,” says the deputy director.

Diana Madrigal, sustainability and wastewater expert, claims that one of the main reasons for the contamination is that the septic systems used in Nosara are not ideal for the district’s type of land.

Experts recommend public sanitary sewage systems in coastal areas, yet Nosara does not have one. Each business or property owner is responsible for installing and maintaining their own sewage treatment system.

Septic tanks are not suitable for coastal areas because of the type of soil and their proximity to the aquifers. They contaminate easily, but the Costa Rican coast is one of the areas where sewage treatment is the worst and the institutions do not offer a sewage solution,” she says.

In places such as Nosara where there is no alternative to septic tanks, Madrigal recommends verifying whether the property soil has adequate filtration capacity and that owners have their tanks maintained as often as one to three years so that they do not overflow or leak.

According to Méndez, the surveillance of septic systems should be a joint effort involving municipalities, the Ministry of Environment and Energy, the Costa Rican Institute of Aqueducts and Sewers (AyA) and the community. 

Situation could damage tourist destination reputation

The ACT deputy director also believes that the tourism sector is directly responsible for collaborating with the institutions in search of solutions, as they “can be most affected by a possible permanent state of water contamination.” “The presence of contaminated waters damages a community’s image. In other words, tourism impacts its own finances,” emphasizes the expert.

Méndez explains that the ocean has enough mechanisms of its own to fight bacteria, whereas the situation in the Nosara River is even more serious because it directly affects the most sensitive species such as river fish and plants.

Contamination implies that less oxygen is produced in the water and, as a consequence, species that cannot survive these conditions quickly disappear,” he says.

Regulation frees institutions of responsibility

According to researcher Bezy, it is currently the responsibility of each person or family to monitor septic tank maintenance. Wastewater expert Diana Madrigal confirms this and adds that the present wastewater management regulation does not designate which institution is in charge of ensuring that owners comply with the regulation.

The WCA analyzed two sections of the Guiones sea: the palm tree sector and near the estuary. For 22 weeks they sampled the waters during the summer and winter of this year. Photo: César Arroyo


At the moment, both the Ministry of Health and the Municipality of Nicoya can act on complaints from neighbors about malfunctioning tanks. They are, however, not compelled to carry out surveillance in the communities.

La Voz de Guanacaste requested an interview with the Municipality and the Ministry of Health regarding this matter, but received no reply at the time of going to press.

In addition, regulations are unclear about which institution can provide solutions in the event of a sewage crisis.

The current regulation places no responsibility on the government concerning wastewater management. There’s no response, we simply do not know who is responsible for responding or intervening in the systems. It’s a problem,” Madrigal stresses.

Community members can report neighbors and businesses to the Health Ministry for not properly maintaining their septic tanks. Complaints can be made by emailing [email protected]. In addition, if you suspect that one of your neighbors is discharging wastewater directly into the river, you can make a formal complaint to the Environmental Administrative Tribunal. For further details, click here.

All the experts agreed that checking the condition of septic systems in your homes is also important at this time. “There may be a problem with your own tank that you are unaware of. That’s why frequent maintenance is so important,” said Madrigal.