High Performance Bioretention Media (HPBM) consists of an 18-inch primary layer containing 60% sand, 20% coconut coir, and 10% high-carbon wood ash (biochar). While this improved bioretention soil media (BSM) offers a higher performance than typical bioretention media containing compost, sustainably sourcing coconut coir, iron filings, and activated alumina remains a challenge. An alternative to HPBM could be to keep the compost in the media and add fungi to attempt to mitigate the export of nutrients and obviate the need for less environmentally sustainable BSM components. Herrera produced this white paper for Seattle Public Utilities to summarize research findings and evaluate the effectiveness and potential consequences of using fungi as a component in BSM for improved nutrient and metals removal.