Although waste stabilization ponds (WSPs) are widely used in developing countries, monitoring data on their operational performance are scarce. Traditional methods for monitoring in-pond conditions, i.e. conducting hand held measurements from a small boat or installing fixed sensor networks, are not straightforward to realize and create an unhealthy working environment for field workers. A promising technology for the safe and efficient collection of monitoring data is a compact autonomous surface vehicle (ASV), capable of autonomous navigation along a predefined trajectory based on geographic coordinates and measurements in different places and depths. In this practical paper, the development process, technical details and functional testing results of a low-cost ASV for WSP monitoring are presented. Commonly available construction materials and electronic components were used to assure affordability and reparability. The access to online tutorials and peer-support was crucial for assembling the open-source autopilot and datalogger. The ASV demonstrated satisfactory performance for both the autonomous navigation as well as the georeferenced data logging of measurements at a real-scale WSP in Paraguay. This study demonstrates how the adoption of open-source hardware and software offers the flexibility for the wastewater professionals to develop customized DIY solutions for specific monitoring applications and working environments.