<p>As the Diavik Diamond mine approaches closure in 2026, the aspirational strategic objective is relinquishment with no requirement for a permanent site presence. The Diavik site is surrounded by a pristine sub-arctic lake, which is one of the main challenges to a successful transition to a passively managed physically and chemically safe post-closure landscape. Several predictive models were developed and connected to assess the performance of the closure plan to prevent any adverse effects to the environment from the closed mine. The models were set up to simulate site runoff quality and quantity, lake circulation, and transport of constituent mass including accounting for the reconnection of pit lakes, one of which is planned as a permanent disposal facility for processed kimberlite, mixing zones within the lake at points of runoff discharge, and lake water levels and outflow rates impacted by pit filling. The differences in bathymetry and time frames of interest for each of these processes required the integration of models with different numerical schemes, timesteps, and spatial domains.The models were developed through an iterative process spanning several years and have provided the information needed to advance remaining regulatory and permitting activities, complete a post-closure human health and ecological risk assessment, and inform ongoing engagement and risk communication strategies. This work has allowed the emphasis to shift from planning and predicting to executing and performance assessment.</p>