The International Great Lakes Datum of 1985 (IGLD85) provides a vertical reference frame for operational, scientific, and emergency management of the Great Lakes water levels. This vertical reference frame uses dynamic heights, which are scaled geopotential values, and makes use of the fact that a lake surface closely follows an equipotential gravitational surface. However, due to significant biases in the leveling data used to construct IGLD85, decimeter biases in water levels exist between gauges on the lakes and Hydraulic Correctors (HCs) had to be added to the individual gauge measurements to ensure equal and consistent lake water levels. In this talk, observations from water gauges on the Great Lakes are combined with GNSS benchmark observations and local leveling data to calculate relative water heights across the Great Lakes. Discrepancies in water heights are found to be on the cm level, an order of magnitude less than IGLD85, and provide updated HCs that will be incorporated in the new IGLD2020 reference frame that is planned to be released in 2027. The impact of different geoid models on the overall results is explored and the newest Canadian/US GEOID22 alpha model is found to perform the best. We also explore the dependence of the result on the method employed for averaging lake levels through time; short-term, long-term, and seasonal averages are compared, and a lake-wide adjustment of water gauge data is used to solve for the HCs of each gauge as well as their relative vertical velocities to other gauges on the lake.