Nutrient clean up is incredibly hard. The life in the water uses the nutrients quickly and exponentially multiply. Watershed restoration can help reduce impacts by increasing wetland and stream health and allowing these ecosystems to take up more nutirents before they enter the lake or ocean. These strategies can take a few years to fully reestablish and must be protected and maintained from invasive species or erosion removing the vegetated portions.

There often are laws and regulations around spreading and even for riparian zones (vegetation next to streams). The places with a lack of regulations for this are often the places nutrient run off is a signifcant issue in watersheds. A lot of the monitoring for my area is done by local watershed conservation groups who share their data with other authorities or authorities in their organization. They often work together with policy makers to find a good balance for the watershed and the economy.

The best preventions for excess fetilizer runoff are

Not using more than needed

Not spreading during wet weather

Ensuring creeks and streams next to the fields are well vegetated around the sides to slow the runoff, absorb nutrients, and slow the water in the creek which slows down the nutrients that do still get in.

There are other more complicsted methods but most follow those guidelines.