Lake Villarrica Decontamination Plan: limits to fish farms and reforestation

The Official Gazette of the Republic of Chile published this Thursday, August 13, in its No. 44,524, the Supreme Decree No. 12 of the Ministry of the Environment, which approves the Decontamination Plan for Chlorophyll “a”, Transparency, and Dissolved Phosphorus for the Lake Villarrica basin, in the La Araucanía Region. The regulation, signed on May 8, 2025, by the President of the Republic, Gabriel Boric Font, and by the Minister of the Environment, María Heloísa Rojas Corradi, imposes emission limits on fish farms, mandatory reports to the Environmental Superintendence (SMA), and forest inspection programs that extend to the communes of Villarrica, Pucón, Curarrehue, and Cunco.

The plan, known as the PDA Lago Villarrica, seeks to recover the levels of the Secondary Environmental Quality Standards for the Protection of Surface Continental Waters of Lake Villarrica (Supreme Decree No. 19, of 2013) within a period of 15 years, extendable. The basin, of 2,805 km², was declared a saturated zone for chlorophyll “a”, transparency, and dissolved phosphorus through Supreme Decree No. 43, of 2017, published on August 6, 2018, and today receives 270.5 tons of total phosphorus per year, 33% above the critical load. The process began in 2018 with Exempt Resolution No. 1,066, included a public consultation with 1,390 observations from 124 people and an indigenous consultation with Mapuche organizations from the basin (48 agreements and 52 disagreements), and was supported by the Council of Ministers for Sustainability and Climate Change through Agreement No. 1, of January 29, 2025.

Emission limits for fish farms

The emission standard for total phosphorus load for the aquaculture sector accounts for 78% of the committed reductions and targets the sector that contributes 26.4% of the lake’s phosphorus: 13 operational fish farms (six in Pucón, four in Villarrica, and three in Curarrehue) that produced 1,922 tons of biomass in 2021. The limits, in kilograms of total phosphorus per year according to production capacity, are:

• Up to 8 t/year: 80 kg/year (existing: from 4 years after publication).
• More than 8 and up to 151 t/year: 560 kg/year (existing: 3 years).
• More than 151 and up to 301 t/year: 1,000 kg/year (existing: 3 years).
• More than 301 and up to 500 t/year: 1,700 kg/year (existing: 2 years).
• More than 500 t/year: 2,100 kg/year (existing: 2 years).

New fish farms must comply from the publication of the decree, and existing ones will have three months to submit a sworn declaration and an adequacy plan before the Seremi of the Environment.

Reports and monitoring before the SMA

Fish farms must report quarterly to SMA, within the first twenty business days, the monthly total phosphorus load discharged to the receiving water body, in addition to a consolidated annual report each March; failing to do so constitutes a sanctionable noncompliance. Effluent monitoring shall be carried out by Technical Environmental Inspection Entities (ETFAs) at least three times per month, and conductivity, pH, dissolved oxygen, temperature, and flow must be measured continuously online. SMA, after consulting Sernapesca, shall set each December the annual inspection program for fish farms in the saturated zone.

Sanitation, reforestation, and forestry enforcement

Wastewater treatment plants serving 2,500 or more inhabitants must comply with a total phosphorus limit of 2 mg/L, with deadlines of 5 or 8 years for existing plants depending on their environmental qualification requirements; the measure includes the new Curarrehue plant, the sewer connection, and rural sanitary solutions. In the forestry sector, Conaf will coordinate a Forestry Enforcement Roundtable made up of the municipalities of Villarrica, Pucón, Curarrehue, and Cunco, Carabineros de Chile, the Regional Ministerial Secretariat for the Environment, and the Lake Villarrica Port Captaincy, which will meet at least twice a year, together with a restoration and reforestation target of 2,000 hectares with native species (1,000 under Conaf’s responsibility and 1,000 with sectoral or FNDR funds).

The instrument estimates benefits of US$3,260.74 million versus costs of US$56.13 million (benefit-cost ratio of 58.09) and projects emissions below the critical load from the fourth year of implementation, with visible water improvements between the fourth and sixth years. Its compliance is mandatory in the saturated zone and safeguards an ecosystem on which tourism depends —Villarrica National Park was the third most visited protected area in the country in 2014— as well as the Mapuche communities of the basin.

Source: Official Gazette of the Republic of Chile, No. 44,524, Thursday, August 13, 2026, Section I, General Standards, pp. 1-40 (official reference: CVE 2852309).