The Freshwater Oil Spill Remediation Study (FOReST) evaluated the effectiveness and environmental impact of enhanced monitored natural recovery following simulated spills of conventional heavy crude oil into shoreline enclosures (5 x 10m) of a boreal lake. Six enclosures, equally divided into treatment and reference groups, were used in this study. Remediation included the flushing of trapped conventional heavy oil and recovery with sorbent pads, and a secondary remediation method referred to as enhanced monitored recovery (eMNR), which includes the addition of nutrients to stimulate microbial and algal oil-degrading activity. Effects were then studied on phytoplankton, biofilm growth and community dynamics over 400 days. Chlorophyll a concentration, ash-free dry mass (AFDM) and algal taxonomy were not significantly different between the treatment and reference enclosures. Therefore, we concluded that the eMNR secondary remediation treatment did not affect the phytoplankton and biofilm community but continued monitoring for eutrophication should be conducted to reduce the risk of environmental degradation.