The transportation of crude oil across Canada leads to a risk of accidental spills into freshwater environments. Conventional cleanup methods can exacerbate the negative effects of oil spills and delay ecosystem recovery. A less-invasive alternative is the use of engineered floating wetlands (EFWs) – vegetated platforms which promote microbial colonization and biofilm formation in their underwater root-zones – to enhance the biodegradation of spilled oil. This thesis assessed the efficacy of EFWs for removing oil-derived polycyclic aromatic compounds (PACs) from fresh water and the effects of plant species composition and nutrient addition carbon to phosphorus (C:P) ratio on EFW function. Twenty-six (26) ~1550 L mesocosms containing EFWs were exposed to equal-volume spills of water-accommodated fraction (WAF) produced by weathering conventional heavy crude oil (CHV). The EFWs were either planted with a different composition of Typha sp., Carex atherodes, and C. lasiocarpa or had an even species composition and were amended with slow-release fertilizer to achieve a target C:P ratio, based on the carbon content of the WAF. Concentrations of PACs decreased rapidly, with 96.8% of compound classes across the mesocosms declining to baseline concentrations within the first 10 days of the 96-day exposure. There was no evidence to indicate that EFWs had an appreciable effect on PAC removal or that changes in plant species composition or C:P ratio affected EFW function. There were no consistent significant effects of WAF, plant presence, plant species, or C:P ratio on the activity of microbial biofilm or the composition and diversity of the prokaryotic and eukaryotic microbial communities in the root-zone. Results were confounded by low initial PAC concentrations, possibility of PAC sorption to mesocosm plastic, flaws in sample event timing, and tadpole grazing on root biofilm; future research which addresses these experimental limitations is required to support the incorporation of EFWs into freshwater oil spill remediation efforts.