The SmartBay Observatory in Galway Bay is an important contribution by Ireland to the growing global network of real-time data capture systems deployed within the ocean. Installed on the seafloor 1.5km off the coast of Spiddal, the observatory uses cameras, probes and sensors to permit continuous and remote live underwater monitoring. Data relating to the marine environment at the site is transferred in real-time from the SmartBay Observatory through a fibre optic telecommunications cable to the Marine Institute headquarters and then made publicly available on the internet. This dataset comprises of processed acoustic data that has been collected from the observatory site using an icListen HF Smart Hydrophone – a digital hydrophone that processes and stores acoustic data. This dataset contains Sound Pressure Level (SPL) measurement data taken by the hydrophone at different frequencies. Practical uses of this dataset includes but are not limited to scientists, researchers and marine technologists involved in the areas of marine mammal monitoring, real-time noise measurement, environmental assessment and improving compliance with the Marine Strategy Framework Directive. Suggested Citation: Gaughan, Paul. (2019) SmartBay Observatory Hydrophone Data (Processed). Marine Institute, Ireland. doi:10/c3jm. Suggested Citation: Gaughan, Paul. (2019) SmartBay Observatory Hydrophone Data (Processed). Marine Institute, Ireland. doi:10/c3jm.