<p>Heavy metal contamination of groundwater is a major challenge to ensuring a safe global water supply. Mn²⁺ ions have become the main contributing indicator of shallow groundwater exceeding Class III water in the Jidong Plain, posing a threat to the local ecological environment and the health of residents. In this study, the distribution characteristics and influencing factors of Mn²⁺ were investigated based on the water chemistry analysis and geological conditions of 171 shallow groundwater samples. The study used mathematical and statistical methods to calculate the background values and found that 66% of the groundwater was unsuitable for direct drinking through the EWQI water quality evaluation method, and the high-Mn groundwater was mainly distributed in the coastal areas. The results show that the migration and enrichment of Mn²⁺ are closely related to the nature of the overburden and the conditions of groundwater runoff. Long-term monitoring of Mn²⁺ content and management measures is recommended to ensure the safety of groundwater quality. The results of this study can provide a scientific basis for further rational evaluation of the shallow groundwater quality and the degree of groundwater pollution in the Jidong Plain.</p>