I think your explanation based on actual observations is about as good as possible. From looking only at the spread sheet over the duration of the thread I could tell that an anomaly was occurring (even though I knew the river and lake were up from the text). I have not seen the clarity jump to that extent at the same time the temps were static and DOs down a little. A very unusual combination absent some large out of the normal event. Just for clarity (of terms and understanding) do you think with the river up you were seeing groundwater influence (water in the underground supply) or river water due to hydrostatic pressure. The 2 could be vastly different in parameters.

How long before you expect the winter plankton to start ?