Uluabat Lake holds a significant status as one of our country's essential Ramsar areas. Nevertheless, the lake faces considerable pressure from environmental pollutants. This study employed GIS-based index methods to examine the heavy metal pollution and water quality in Uluabat Lake. To achieve this, sediment and water samples were collected from 19 different locations during various seasons. The concentrations of As, Ni, Cr, Zn, Cu, Cd, Pb, Hg, Al, Fe, and Mn in these samples were analyzed. The average contents of the investigated heavy metals in the lake waters were found to be in the following order: Al > Fe > Mn > As > Zn > Ni > Pb > Cu > Cr > Hg > Cd. The As content in the lake waters exceeded the limit value of 10 μg/L, as defined by TS-266 (2005) and WHO (2017) guidelines. Consequently, the lake waters were deemed unsuitable for drinking. The health risk assessments revealed that consuming the lake waters could lead to both carcinogenic and non-carcinogenic health problems. However, all other metal concentrations were measured below the specified limit values. Based on index calculations, the heavy metal pollution index value indicated that the lake water samples were suitable for drinking water use. Additionally, all samples fell into the "low pollution" category according to the heavy metal evaluation index, and degree of contamination values. However, geoaccumulation index values indicated that As was moderately contaminated. Moreover, enrichment factors of As, Cr, Ni, Pb, and Cd exhibited significant enrichment in lake sediments, with pollution load index values of all sediment samples indicating the impact of anthropogenic pollutants and a decline in sediment quality. Considering all the obtained results together, it can be concluded that environmental pollutants, especially heavy metal pollution, primarily enter the lake water through stream transports, leading to pollution in Uluabat Lake.