Since 1968, year of the May Revolution in France, UNESCO realised that a rapid separation was developing between the human race and nature, especially in big cities. This resulted in the development of numerous Environmental Education Programmes for children. Tench fishfarms are a particularly good tool for educating children in the structure and function of freshwater ecosystems. The 'Vegas del Guadiana' fish farm (Badajoz, Spain) Environmental Education Programme, is included in the Transborder Environmental Education Programme and in INTERREG II, an European Community Initiative whose objective is to promote cross-border, international and interregional co-operation to encourage balanced development in Europe. Preliminary results have been evaluated and presented in the present work. The analysis of the efficiency of the programme was measured in children from ages 6 to 12. The results showed no significant differences among sex (t-Student=0.07, p=0.9470) nor social surroundings (t-Student=0.87, p=0.3910) but there were significant differences when comparing different ages (ANOVA, p=0.0437). In all cases, a significant increase in the knowledge and concern about the freshwater environment was found in children (Paired t-Student=)10.55, p=0.0001).