text: Since many algal blooms are caused by a major influx of nutrient-rich runoff into a water body, programs to treat wastewater, reduce the overuse of fertilizers in agriculture and reducing the bulk flow of runoff can be effective for reducing severe algal blooms at river mouths, estuaries, and the ocean directly in front of the river's mouth.
  The nitrates and phosphorus in fertilizers cause algal blooms when they run off into lakes and rivers after heavy rains. Modifications in farming methods have been suggested, such as only using fertilizer in a targeted way at the appropriate time exactly where it can do the most good for crops to reduce potential runoff. A method used successfully is drip irrigation, which instead of widely dispersing fertilizers on fields, drip-irrigates plant roots through a network of tubes and emitters, leaving no traces of fertilizer to be washed away. Drip irrigation also prevents the formation of algal blooms in reservoirs for drinking water while saving up to 50% of water typically used by agriculture.
  There have also been proposals to create buffer zones of foliage and wetlands to help filter out the phosphorus before it reaches water. Other experts have suggested using conservation tillage, changing crop rotations, and restoring wetlands. It is possible for some dead zones to shrink within a year under proper management.
  There have been a few success stories in controlling chemicals. After Norway's lobster fishery collapsed in 1986 due to low oxygen levels, for instance, the government in neighboring Denmark took action and reduced phosphorus output by 80 percent which brought oxygen levels closer to normal. Similarly, dead zones in the Black Sea and along the Danube River recovered after phosphorus applications by farmers were reduced by 60%.
  Nutrients can be permanently removed from wetlands harvesting wetland plants, reducing nutrient influx into surrounding bodies of water. Research is ongoing to determine the efficacy of floating mats of cattails in removing nutrients from surface waters too deep to sustain the growth of wetland plants.
  In the U.S., surface runoff is the largest source of nutrients added to rivers and lakes, but is mostly unregulated under the federal Clean Water Act.  Locally developed initiatives to reduce nutrient pollution are underway in various areas of the country, such as the Great Lakes region and the Chesapeake Bay. To help reduce algal blooms in Lake Erie, the State of Ohio presented a plan in 2016 to reduce phosphorus runoff.