We present a low-cost sensor buoy designed for unattended dissolved oxygen measurement in aquatic environment. We describe the buoy’s architectural design and three experiments that we carried out to demonstrate its viability: a laboratory test in a water tank with controlled oxygen level, a lake deployment and an extensive electric power consumption test. Our experiments indicate the viability of such an approach to dissolved oxygen monitoring and promise further advances in hypoxia studies. Department of Computer Science Kent State University Technical Report: TR-KSU-CS-2009-01