In Brazil, domestic effluents represent the primary source of pressure on water resources. Water pollution can be controlled by defining, applying, and enforcing the effluent standards for wastewater discharge. Discussions are ongoing in Minas Gerais State regarding the possibility of setting a discharge standard for ammonia nitrogen in municipal wastewater, which is currently not required. However, providing technical support for decision-making is challenging because of the difficulties in accessing monitoring data from sewage treatment plants. This study aimed to analyze the monitoring data from 49 sewage treatment plants operating in Minas Gerais to offer guidance for decision making. High concentrations of ammonia nitrogen in the effluents of the treatment plants were found, reinforcing the need for better control and the adoption of more advanced technologies. Furthermore, it was observed an increase in concentrations downstream of the discharges in the receiving water bodies. Adopting a progressive and adaptable discharge standard can be a solution for better control of treatment systems.