In a eutrophic lake, visiblity 18" or less and max depth of 30-40 feet, how long after the spring turnover do you expect to find a dead zone?
I just reveiwed my ecology text book on the matter of lake stratification and the resulting dead zone.
If light penetrates the thermocline into the hypolimnion then the rooted plants supply oxygen to all layers of the lake and you will have life throughout the lake year round. If light doesn't penetrate below the thermocline, you will get a dead zone.