Last week Joanna and I went snorkelling in Coles Bay. We were there alone at night, having been inspired by swimming there with a large group the night before to look at the seasonal bioluminescence.
The last time I had been there was in December of 2020 so, just based on the normal seasonal variations for Saanich Inlet, I was expecting the visibility to be worse but the opposite turned out to be the case. Looking back over my notes I was reminded that in winter there had been a steady flow of freshwater from the surrounding storm drains. By itself freshwater is less dense than saltwater and has a different refractive index for visible light so when the two are turbulently mixed the view through them is cloudy.
On the winter visit I had to dive below the halocline to get into clearer water but there was no need to leave the surface last week, especially since we were there to watch the bioluminescent sparkles from our hands and fins.