In different Mediterranean zones (MZ) of the world, extensive areas of native forests have been replaced by forest plantations composed of non-native species that exceeded 264 million ha globally in 2010. In Chile, 80% of these plantations are distributed in the same zone where forested wetlands are dominant. Non-native forest plantations are inversely related to the quantity, distribution and availability of water resources. In this study, the characteristics of the water regime of the forested wetlands were assessed, and their relationship to non-native forest plantations and native forest cover was established. The results indicated that most forested wetlands present a significant decrease in both depth and water volume in the summer (p < 0.05), which is related to a decrease in rainfall. However, those wetlands with a higher percentage of non-native forest plantations in their basins (> 18%) presented a temporary water regime, unlike those in which native forest dominated (>21%), which presented a permanent water regime. Strong negative relations were registered (p < 0.05) among the percentage of forest plantation and water availability, minimum depth and minimum water volume. On the other hand, the percentage of native forest was positively related with the same variables (p < 0.05). This study presents a clear relationship between forest activity and water availability, especially during the summer, when the normal decline of the water resources in the wetlands worsens.