Polarised green sea

On Scilly, the sea was noticeably green in many places, mainly shallower bits. Here at Old Town on St Marys I realised that the water looked green when I was wearing my polarising filters but not so much without. The top picture shows without, the middle picture shows the greenish tint through the filter and the bottom is the filter through 90 degrees. This green colour is clearly plane polarised. I had come to the conclusion some time ago that the colour of the surface of the sea is usually a reflection of the sky colour. Polarisation by reflection is common above the Brewster Angle. However the sky wasn't green so I don't think that's happening here. NASA suggest that green sea is due to phytoplankton https://science.nasa.gov/earth-science/oceanography/living-ocean/ocean-color I don't know if that is likely so close to the shore.