The OPTAIN project developed a decision-support methodology and tools to help identify the most suitable Natural/Small Water Retention Measures (NSWRMs), their combinations and optimal locations in agricultural areas. The approach enables the comparison of different implementation scenarios, taking into account local soil, climate, hydrological and farming conditions, as well as the environmental effectiveness and economic aspects of the measures. The practical value of the innovation for farmers is the ability to make more informed decisions about which water and nutrient retention measures to apply, where to apply them and what effects can be expected. These measures may include cover crops, reduced tillage, buffer strips, small wetlands and other water retention solutions. In Lithuania, the methodology was applied in the Dotnuvėlė catchment, where different measures and their combinations were modelled and their effects on water retention and nutrient and sediment losses were assessed. Farmers, agricultural advisers and other local stakeholders were involved in the process, linking scientific assessment with the practical feasibility of implementing the measures. Although the measures are optimised at catchment level, their practical implementation takes place on agricultural land and farms. OPTAIN results help farmers and advisers select solutions suited to local conditions, improve water and nutrient retention, reduce losses and increase farm resilience to droughts and heavy rainfall. Practical recommendations and project results are available in the NSWRM implementation guidelines and the OPTAIN Learning Environment.