Lake Miwasin is a demonstration-scale pit lake project that implements a �Permanent Aquatic Storage Structure� (PASS) to treat mine tailings, which are subsequently stored at the bottom of the lake. Lake Miwasin requires levels of water high enough to maintain a threshold freshwater cap over the tailings and the surrounding upland has been designed to contribute water to the lake for this purpose. In recent years, small marsh-like wetlands dubbed �opportunistic wetlands'' have spontaneously appeared on this site. The study of these wetlands on other sites is limited to a few papers and further understanding as to their function, controls on their permanence, and formation is needed. Should these wetlands not be able to sustain their saturation, there would be great loss of diversity to the reclaimed site. There is also concern that these wetlands are evapotranspiration (ET) windows, leading to a loss of water in the system, potentially causing unstable lake levels, posing risk to the functioning of the system and requirements regarding exposure of the mine tailings. This project investigates opportunistic wetlands appearing at Lake Miwasin, identifying their role in the water budget and their influence on water levels in the pit lake. To accomplish this, a water budget and water use efficiency for the opportunistic wetlands is presented. Preliminary results indicate that ET is the largest component of the water budget for the wetlands while groundwater flow is limited due to low hydraulic conductivity values from highly compacted mineral material.