The declining water level in Great Salt Lake (GSL) has been attributed to human consumptive water use that depletes natural streamflow into the lake. Understanding depletions due to historical consumptive water use within the GSL Basin is important to managing present and future lake conditions. Direct calculations of consumptive water use in the basin are made by summing detailed uses and return flows. However, this method is limited by insufficient data and resulting estimates thus far have been disparate. In this study, we reconstructed total GSL water inputs and stream inflows using lake levels recorded from 1847-2023 to estimate the magnitude of reductions due to consumptive use and the associated lake level decline. To do so, we developed a method that uses lake volume changes derived from bathymetry and water surface elevation measurements along with estimates of annual evaporation and precipitation over the lake to hindcast inflow volume to the lake. The declining trend in lake inflow, without associated precipitation or natural streamflow trends, was used to quantify basin wide water depletions to be up to 2.3 km3/yr and the current lake level decline associated with this estimate to be as much as 4.6 meters. This basin wide depletion estimate depends only on lake level, precipitation, and evaporation estimates and is not limited by the challenges of aggregating individual diversions and return flows.