Executive Summary

The Federal Department of Defence, Civil Protection and Sport (VBS) collected lake water samples from Lake Thun, Lake Brienz, and Lake Lucerne again in autumn 2024 and winter 2025. These lakes contain submerged ammunition from army stocks that was disposed of until the mid-20th century. Analyses of approximately 60 samples show no negative impact on lake water from the submerged explosives. Pollutant concentrations remain stable or declining compared to earlier measurements.

Persons

Topics

  • Environmental monitoring
  • Water protection
  • Legacy site management
  • Drinking water safety

Clarus Lead

The monitoring result defuses a long-standing uncertainty: despite the high pollution potential of the submerged ammunition, no measurable contamination is evident in practice. For cantons and water suppliers, this means that the existing surveillance strategy is working and no remediation measures are required. The stable to declining trend across multiple measurement campaigns confirms that explosives and heavy metals are not reaching drinking water reserves in problematic quantities under current conditions.

Detailed Summary

The submerged ammunition dates from a time when disposing of ammunition stocks in lakes was a common practice worldwide. A comprehensive hazard assessment by the VBS in 2012 acknowledged the theoretical pollution potential but found no relevant explosives in lake water even at that time. Due to the importance of these bodies of water as ecosystems and drinking water reserves, the VBS, the Canton of Bern, and the Lake Lucerne supervisory commission decided on periodic monitoring.

The latest investigations analyze a broad spectrum: explosives such as TNT and nitroglycerin, perchlorate, and heavy metals (lead, mercury, zinc, copper). Concentrations are almost uniformly near or below the detection limit. According to the Contaminated Sites Ordinance, the ammunition areas are registered in the VBS's contaminated sites cadastre but require neither monitoring nor remediation. The current monitoring frequency—five years for lake water, ten years for lake sediments—will be maintained and reassessed after each campaign.

Key Findings

  • Lake water samples from three Swiss lakes show no contamination from submerged ammunition
  • Pollutant concentrations are stable or declining since earlier measurements
  • No remediation measures required; existing monitoring concept has proven effective

Critical Questions

  1. Detection Limits and Detectability: Are the analytical methods used sensitive enough to detect potential future releases early, or could pollutant concentrations remain below the detection limit?

  2. Long-term Trends and Climate Change: How robust is the assumption of stable conditions given temperature changes and altered lake circulation patterns that could accelerate sediment remobilization?

  3. Spatial Representativeness: Do the 60 samples cover all critical zones, particularly in the immediate vicinity of ammunition depots, or are measurements concentrated on less contaminated areas?

  4. Sediment Contamination and Food Chain: The report emphasizes lake water, but what is the situation in lake sediments, and is there risk of bioaccumulation in fish or other organisms?

  5. Cost-Benefit of Recovery: Has a cost-benefit analysis been conducted for recovery versus long-term monitoring, or is monitoring accepted as a permanent solution?

Source Directory

Primary Source: Explosive Substance Monitoring 2024/25: No Negative Impact on Lake Water from Ammunition – news.admin.ch, 07.04.2026

Supplementary Source:

Verification Status: ✓ 07.04.2026

This text was created with the support of an AI model. Editorial responsibility: clarus.news | Fact-checking: 07.04.2026