The City of Coos Bay constructed its first Wastewater Treatment Plant, now known as WWTP1, in 1950. The plant included a control building, grit channel, clarifier, and anaerobic digester. Along with the construction of the treatment plant, collection lines were installed and pump stations were constructed. The plant was built in response to the Federal Water Pollution Control Act of 1948, which made it unlawful to  discharge any pollutant into navigable waters without a permit.

WWTP1 was upgraded in 1972-1975 to include an additional digester, chlorine building, aeration basins, grit collector, and a final clarifier. These upgrades were due to the Federal Water Pollution Control Act Amendments of 1972, popularly known as the Clean Water Act, which established national standards for sewage treatment and significantly increased federal funding to help communities meet the laws. The Clean Water Act established the National Pollutant Discharge Elimination System (NPDES) permit program, which controls water pollution by regulating point sources that discharge pollutants into waters of the United States and setting discharge limits to protect waterways and improve water quality.

Wastewater treatment plants typically require major updating every 15-20 years in order to stay in compliance with DEQ requirements. WWTP1 was upgraded again in 1990, including building a new primary treatment area and secondary clarifier, remodeling the maintenance building, and updates to the aeration basins, digesters, grit system, headworks system, chlorine contact basin conversion, outfall repair, and a large electrical upgrade to the plant. In the planning of this upgrade, consideration was given for future upgrades so there was space intentionally left open for future needs of the treatment system.

WWTP1 is undergoing an upgrade; construction began in 2023 and will take three years.