Answer:
It is a chronic effect of a toxin in the lake.
Explanation:
Not only did I take the test and it was right but a chronic effect is an adverse effect on the human or animal body (in this case human) with symptoms which develop slowly over a long period of time.
In short terms, chronic is long-developing (every day of summer can be considered a long-developing time) while if it were acute it would be quick and sudden.
We also know its not a synergistic reaction because that would mean Kris was exposed to the effect of two or more chemicals at the same time and we don't have enough data to confirm that. It's also not an antagonistic reaction to a toxin because that would mean Kris was exposed to the effect of two or more chemicals at the same time that lessened the sums of their effects.
So, by process of elimination it's "a chronic effect of a toxin in the lake."
