Extremely worrying Very high pesticide residues measured in the Wyna

Very high levels of pesticide residues have been detected in the River Wyna in the canton of Lucerne. The high deltamethrin levels are extremely worrying.

Keystone-SDA

11.01.2026, 18:59

SDA

The canton of Lucerne has detected very high pesticide residues in the River Wyna. For the Federal Department of the Environment, Transport, Energy and Communications (DETEC), the high deltamethrin levels in the Wyna are a cause for concern. The pesticide active ingredient may only be used in exceptional cases.

The "NZZ am Sonntag" initially reported on this and referred to a letter from the canton of Lucerne to farmers. In it, the canton stated that "very high concentrations" of the active ingredient deltamethrin, which is highly toxic to fish and insects, had been detected during measurements in the Wyna between September 8 and October 8, 2025.

Threshold value exceeded up to 4200 times

The authorities wrote that the values were hundreds and even thousands of times too high. When asked by the "NZZ am Sonntag", the canton stated that the highest value measured exceeded the ecotoxicological threshold value by up to 4,200 times. The newspaper points out that the Lucerne Agricultural Office approved the treatment of rapeseed fields in the region with deltamethrin during precisely this time window in the fall.

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At the request of Keystone-SDA, the Uvek confirmed statements to the "NZZ am Sonntag" that the high deltamethrin levels in the Wyna are a cause for concern and are being taken seriously. There are legally binding requirements for the protection of water bodies for all approved plant protection products.

The cantons must monitor compliance with these requirements. If the limit values are exceeded, they must take measures, wrote a media spokeswoman for the Federal Office for the Environment FOEN, which is part of the Federal Department of the Environment.

Use only if there is no alternative

According to the letter, deltamethrin is one of the active substances whose use has been banned for farms entitled to direct payments since January 1, 2023.

Deltamethrin may only be used if it cannot be replaced by active substances with a lower risk to the aquatic environment. "There are currently no equivalent alternatives to protect certain crops; the active substance is therefore currently important for agriculture," the Uvek continued.

The Water Protection Ordinance currently sets limits for 19 pesticide active substances. The Federal Council wants to set new ecotoxicologically based limit values for seven more. For three other active substances, one of which is deltametrin, the Federal Council is refraining from setting new limits for the time being.

The Federal Council opened consultations on the amendment to the Water Protection Ordinance on November 26, 2025. According to Uvek, the Federal Council intends to review the situation again once this consultation is complete and set a specific limit value for deltamethrin in a next step.