Three years ago a fancy new nitrate-retention pond was built. The idea was for all the field drainage to collect in a wetland. to use up any excess nitrogen before tumbling away downstream and off to a river. This is what the upper pond looked like three years ago.
There also was extensive grasslands around the ponds, but when we went to visit this year, most of those were plowed back up, after having been seeded to native plants just three years ago. Now, the lower pond shows signs of very high nitrogen (excess nitgrogen applied to farm fields and washed away). The masses of floating algae lumps have taken over the water.
Unfortunately, most of the field drainage tiles lines are not fed into ponds like this and all that nitrogen is heading straight to the rivers and the dead zone in the Gulf of Mexico.