Wildlife pond - slightly 'milky' water?

Hi,

Our frogspawn has hatched and they look fine. But unless it's a trick of the light, the pond water looks very slightly 'milky'. I remember this happening in other year and it coinciding with time I introduced an oxygenator, I assumed perhaps wrongly that it was down to the oxygenator. This year i've introduced it a couple of weeks ago, it didnt happen straight away, but has now. It maybe totally unrelated! Anyone any clue or am i worrying over nothing?

Thanks in advance