Sampling aquatic ecosystems is a laborious and expensive task, especially when covering large areas. This can be improved using unmanned aerial vehicles (UAVs) equipped with various remote sensing sensors. However, the UAV performance and autonomy may vary due to external factors when it is operated outdoors. In some cases, an emergency landing maneuver is necessary to avoid an accident, since in fluvial environments, the UAV control landing becomes a difficult operation. Therefore, it is important to have a backup platform on the water to fix this problem. This paper presents the design and development of a custom-built unmanned surface vehicle using open-source tools and with two types of operation—remotely piloted and autonomous—to support remote sensing practices with UAVs in fluvial environments. Finally, part of the software developed within this project was released in an open-source repository.