A simultaneous shift has occurred in lakes across West Greenland. At some point since August 2022, lakes that were “blue” or very clear for decades have rapidly and darkly turned brown. Unusually wet and cloudy conditions over the past year likely led to this change in lake color, but the factors contributing to this color change remain unclear. Preliminary data suggest that metal concentrations have increased by an order of magnitude in these lakes, and a similar change in water color has been observed recently in streams in the Brooks Range of Alaska, raising the question of whether this will become a pan-Arctic phenomenon, leading to widespread changes across Arctic freshwater systems. A key initial step to understanding this major change is to quantify what factors are contributing to this color change, and what their origin might be. This proposed work aims to contribute to the broader understanding of this phenomenon.<br/>The rapid, substantial change that we observed in these lakes presents yet another example of how changing climate threatens the ability of Arctic communities to ensure safe drinking water sources. We will analyze water and sediment samples from the drinking water source of Kangerlussuaq, Lake Ferguson, to analyze trace elements, including lead and arsenic, to assess whether these have changed as a consequence of the recently altered hydrology. This work aligns with priorities set forth in Greenland’s National Research Strategy by promoting international cooperation and communicating results in multiple ways to make it broadly accessible. The research will also be of benefit to other Arctic communities by identifying potential emerging threats to drinking water. This project will also provide support for a Ph.D. student and an early career scientist.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.