https://phys.org/news/2018-06-heavier-manure-algae-blooms.html

Phosphorus, a nutrient found in the manure applied to agricultural fields, makes its way to Wisconsin waters (and waterways elsewhere) in runoff following rain storms. When the weather is warm, it can lead to the foul-smelling water and toxic algae blooms that plague lakes like Mendota, which is situated in an agricultural landscape.

This runoff may be getting worse, according to a recent study from researchers with the Water Sustainability and Climate Project at the University of Wisconsin–Madison. With a changing climate, the frequency of high-intensity rain events is on the rise. These storms bring heavy rains over a short period of time and exacerbate phosphorus runoff from manure-covered agricultural fields, more so than scientists expected.