This paper presents our recent advancements in the development of the underwater optical wireless modems, designed within the OptoCOMM project. The target performance of the optical modem is to achieve the data rate of 10 Mbit/s at a distance of at least 10 m in presence of sunlight. The transmitter is based on blue Light Emitting Diode (LED) technology. The modem will be developed in three versions to be integrated in Littoral Ocean Observatory Network (LOON) test-bed, and add a novel technology to the infrastructure of the FP7-SUNRISE project. We tested the first version of the modems in a typical shallow harbour water (1 m depth), in the same location of the LOON to validate the adopted technology. The seawater of the test-bed is characterized by a medium-high turbidity (about 1 FTU), which heavily affects the optical communication in terms of attenuation. All tests were run in sunny summer days with very high sunlight illumination level (∼ 100 klux). Despite the challenging conditions, we achieved successful transmission at 10 Mbit/s over 7.5 m distance.