Masses of microscopic plants called algae clouded the water over the summer months, and the broads filled up with soft mud. The number of fish species and the age of fish declined, as did the variety of wildfowl. This condition is known as phase 3 . In order to restore clear water and wildlife to broads which have deteriorated, it is essential to reduce the levels of nutrients in the water. Research has shown that recovery of aquatic life depends on a dramatic reduction in either the nitrates or the phosphates.
Phosphates come mainly from human sewage.
Sources of nitrates are more widespread and varied, so work has concentrated on removing phosphates. Recent research has also shown that phases 2 and 3 are alternative states, so a broad can be dominated by algae or clear and full of plants at low to medium nutrient levels. There are a number of biological factors which tend to hold a lake or broad in either state and it is necessary to manipulate these in order to cause a switch from one to the other. This is called biomanipulation . Microscopic animals, such as water fleas, are vital to the re-creation of clear water.