Something we get here on Lake Erie is a botulism outbreak. Plant matter pools in a low spot out of the current and decays to the point where Anaerobic respiration occurs. Botulism bacteria need this condition. As the fish feed into this area they die off and sink into the area. Repeating the process as other things feed into the area and also die until the area is flushed out by the current thus ending the cycle. A large pool of "dead" water can move like a curtain and kill across a large area. I remember seeing a few of the mass die offs on Cayuga as a kid in the 80's. Remember the duck die off in Stewart Park. Same concept. As the local business' use the lake as a big heat exchange for their air conditioners the lake has to absorb more heat energy and thus enabling production of more plant matter. More than the end of the lake can naturally flush out. It would be interesting to see what is being flushed, run off, into the lake as the winery industry increases and the farms decrease. Different fertilizers and nutrients being fed into the streams in the area that might enable a bloom in algae and bacteria in the lake to explode.