Lake Mendota, seen from the air, looks pristine on a foggy morning. But a new study suggests it could literally take centuries for the lake to regain its natural chemical balance. Limnology graduate students wade through a blue-green algae bloom in this 1994 file photo. Blooms kill fish and create foul-smelling water that plagues Lake Mendota in the summer. The phosphorus that causes these problems comes from excess agricultural and lawn fertilizers and animal waste.
Students collect water samples with a seine.
A new university study of what happens to all the agricultural run-off pouring into Lake Mendota suggests it could literally take centuries for the lake to regain its natural chemical balance. Phosphorus is the culprit behind many water-quality woes in the lake. The problem for Mendota, and for most watersheds in agricultural settings, is that what goes into the watershed isn't necessarily coming out. The budget found that a huge amount of phosphorus accumulates in the watershed's soil every year. Most phosphorus comes from excess agricultural and lawn fertilizers and animal waste, which land managers generally call non-point source pollution.