It looks like a turnover. I thought it happened twice a year in the process of heating up and cooling down. Here is a quote from anothe site on turnover.

A lake in turnover is very turbid or murky. It is not uncommon to have good success at a lake one weekend and return the next weekend to find less than 30 centimetres of visibility. The water will be filled with all kinds of plant matter floating, and the fishing will be poor. Surface winds cause the lake to mix from top to bottom. This results in mixing of oxygenated and un-oxygenated water and release of other gases that affect fish physiology.

Maybe it won't last long.