Thanks to Interreg funding and transnational cooperation, TRUST ALUM helped overcome barriers to the use of ALUM treatment in Estonia, Latvia and Lithuania. By demonstrating the effectiveness and safety of ALUM treatment, the project built trust among public authorities, experts, and other organisations, and launched a permanent expertise hub that connects practitioners and researchers across borders. The pilot generated valuable evidence and provided a practical example that can encourage the wider use of ALUM treatment across the Baltic Sea region. As a follow-up to the pilot activity, the project plans to monitor water quality parameters in Lake Velnezers in Latvia for at least the next five years.

By transferring proven solutions across borders, the project has created lasting capacity for more effective lake restoration and eutrophication management across the region.

One of the project’s greatest achievements was contributing to regulatory changes in Latvia. The project’s pilot activities, scientific evidence, and dialogue helped pave the way for amendments to existing regulations that recognise ALUM treatment as a valid measure to improve water quality. This removes a key barrier to future implementation and creates favourable conditions for wider uptake of the method.

Can a boat save a lake? 

500 kilometres to carry a solution

Lake Velnezers in Riga, a popular recreation area, was turning greener and murkier every year. An excess of nutrients trapped in the lakebed was fuelling algae blooming. But it was more than an aesthetic problem: in winter 2024, the lake suffered a major fish kill as oxygen levels plummeted.

The solution for this eutrophic lake came from Sweden. Through the Interreg project Trust ALUM, a specially designed Swedish boat brought a restoration method that has been improving water quality in Swedish lakes for decades. Over three days, 12 tonnes of aluminium salts were precisely applied to the lakebed, while water quality was monitored every hour. The treatment permanently bound phosphorus in the sediments, preventing it from feeding new algae blooms. Within just a month, water clarity improved from 0.7 metres to 2.6 metres, and within a year, phosphorus concentrations dropped by over 75%.

This pilot activity did more than help restore one lake. It showed that proven solutions can travel across borders. “Applying new, innovative methods to improve the environment is both exciting and essential for protecting our natural resources,” said Mārcis Zariņš from Riga City Council. The demonstration also resonated beyond Latvia. “The achievements of Trust ALUM in Latvia will inspire the continuation of such activities in other Baltic countries,” said Vaiva Ramanauskienė from the Environmental Centre for Administration and Technology in Lithuania. Throughout the project, authorities and practitioners from Estonia, Latvia, Lithuania and Sweden worked together to build confidence in the method and learn how it could be applied in different national contexts. The impact of transnational cooperation is already visible – from cleaner water in Lake Velnezers to Latvia taking steps to officially recognise ALUM treatment as a lake restoration measure.