Beginning in 2019, Soundnine Inc. (S9) collaborated with Caribbean Wind LLC in the Chesapeake Bay Trust Hypoxia Project to pilot a cost effective, real-time dissolved oxygen monitoring system using a lightweight, low-power, real-time inductive CTD-O2 mooring with sensors at multiple vertical measurement levels to profile dissolved oxygen concentrations. The linked project presentation (2019) provides details on the proposed tasks for this project and expected outcomes and deliverables. S9 integrated a PME optical dissolved oxygen sensor with the newly developed XIM-CTD and delivered a ready-to-deploy Ulti-Buoy mooring to Caribbean Wind in Spring 2020. The first mooring in 22 meters was deployed on May 30 and recovered on June 19 from a 19-foot outboard skiff with a 2-person crew. Caribbean Wind reported first results and impressions on June 24. The mooring was re-deployed from September 13 to October 8. Caribbean Wind’s second interim report report on 15 October is most encouraging. A prime objective of the project was to assess the reliability of deployed equipment and sensors and reliability of data and infrastructure that sustains the deployment. The second test deployment provided high quality data and a rather stunning demonstration of system reliability. “During the 25-day deployment, the 4-instrument mooring showed a 99.6% ( 14100/14164 instrument records) data return, with all sensors reporting all variables for the entire time. The intent was to leave the mooring out through October, but on 06 October around 0900Z, data transmission was interrupted, resuming about 3 hours later, 3.75 nm NNE of the deployment site. Caribbean Wind was notified on 7 October that the buoy had been run over by the Atlantic Surveyor (a vessel on hydrographic survey contract to NOAA), entangled in a side scan sonar cable, and released and left near the entrance to the Choptank River channel. This dragged the mooring from 22 m depth to approximately 14 m depth, at a speed of over 1 knot. While the buoy did not transmit or receive GPS data during this time – it was likely underwater – it did still continue to collect data from the sensors. The buoy was recovered, fully intact and operational except for damage to the urethane foam float covering, on 8 October.” The following plot shows Dissolved Oxygen data recorded at 10-minute intervals, with 1-meter linear vertical interpolation between surface (1 m) and bottom (20 m) sensors. Black lines are locations of Soundnine XIM-CTD-DO real-time sensors, and grey lines are locations of internally recording sensors (SBE 37-ODO). The lower half of the water column was uniformly hypoxic at the outset, but tides and winds gradually mixed oxygen into the lower water column.