Does it have something to do with temp?
what is the question?
Excess use of fertilizer will not be taken up by the plants and can therefore dissolve into water. This water can become runoff and wash into lakes/rivers/streams. Now the fertilizer is a food for algae. As they die and decompose, the bacteria will use the oxygen in the water (cellular respiration). This eutrophication is more common in the summer because hot/warm water holds less oxygen than cold.