"Studies show that 19% of the phosphorus in our lakes comes from construction site erosion."
We've been asked for the source of this data...
The figures below are for Lake Mendota.
"Inventory and modeling produced estimates of sediment and phosphorus loadings to the lake (see Table 1). Several surprising findings emerged from the planning work. The first was that although less than 1 percent of the land area was undergoing development, models suggested that portion of land accounted for almost one quarter of the sediment loading and one fifth of the phosphorus loading to the lake (WDNR 2000)." Source