The subaqueous disposal of reactive mine wastes in Mandy Lake, Manitoba was asessed. Water, sediment, benthos, zooplankton and phytoplankton were collected at four stations, and were analysed. An abundance of organic material was found in the lake. Lake biota were examined and aquatic vegetation in the lake was collected and analysed for metals. Several appendices, dealing with topics such as dissolved oxygen and temperature profiles and petrographic analyses, were included in the report.