The preservation/restoration of natural environment is frequently entailing excessive cost (paid by people through taxation) while it is a source of additional income for both, the State and the people, due to tourism. Since the evaluation of this good cannot be in market terms, we apply herein a modified version of the Contingent Valuation Method (CVM), used in Experimental Economics to investigate the significance that people put on this good and how much they might be willing to pay (WTP) for supporting activities concerning the preservation/restoration of three lakes in northern Greece. The WTP dependence on (i) external diseconomies, (ii) the expectations for property values' rise as a result of the restoration, (iii) the proximity of interviewees' residence to the lakes, and (iv) the time and money that the interviewees spent to visit the lakes, are estimated by means of Logit, Probit, Logistic and Linear Regression Models.