The Vihti Water Resources Day took place on 4 December 2024 in Vihti, Finland, bringing together around 50 stakeholders to discuss the ongoing challenges of nutrient management and lake restoration. The event provided a forum for knowledge exchange on both scientific research and practical measures to address internal loading and eutrophication in Finnish lakes.

Olga Tammeorg (University of Helsinki) presented research on sediment phosphorus and its potential as a fertiliser, drawing on preliminary results from one of FERRO’s WP9 study area, Lake Enäjärvi. The presentation highlighted how phosphorus that has accumulated in the bottom sediments of lakes can be released back into the water when oxygen levels drop, creating a cycle that accelerates eutrophication. Tammeorg shared insights on the spatial distribution of phosphorus in Enäjärvi, noting that the largest accumulation areas appeared to be in the northeastern part of the lake.

The event included discussions on whether management approaches such as active fishing could be sufficient to improve the ecological status of Enäjärvi, or if more extensive interventions would be necessary to prevent further internal loading. Historical examples, such as the suction dredging carried out in Gallträski, Kauniainen, between 2009 and 2011, demonstrated that removal of phosphorus-rich sediments can significantly reduce water phosphorus concentrations and accelerate lake recovery. Challenges associated with sediment removal and utilisation were also highlighted, including high costs, potential environmental harm and contamination with heavy metals.

The day concluded with a presentation of 3D flow modelling for Lake Hiidenvesi, commissioned by LUVY, showing how deepening shallow straits in the northeastern part of the lake could influence water turnover, nutrient transport and overall water quality. The modelling prompted discussion on the economic feasibility and ecological effectiveness of dredging, as well as its potential to mitigate internal nutrient loading while complementing reductions in external nutrient inputs. The event was covered on LUVY’s LinkedIn page and website, reflecting strong interest in innovative approaches to sustainable phosphorus management and lake restoration.