An investigation by the Environment Agency will measure how much of a nutrient which causes excessive weed growth is present in the River Nene.
The Environment Agency is working with the British Geological Survey to evaluate levels of phosphate in the Cambridgeshire and Northamptonshire river.
Starting today (Tuesday 26 February), silt samples will be taken from a 60-mile stretch of the river between Badby and Peterborough and then examined.
Rob Price, of the Environment Agency, said: “We will be collecting and analysing silt samples from the river bed.
“This will show us what level of phosphate is trapped in the silt and allow us to model the rate at which it becomes available to algae and plants.
“The information will be used to determine what future works are needed on the river to improve the quality of the environment.
“Rapid and excessive plant growth can have a negative impact on the natural water environment.”
Phosphate is an essential nutrient for plant growth and is available naturally in very small quantities.
It is mined and used in agriculture to help grow crops and other foodstuffs. It is also used with other chemicals in domestic detergents, often to soften water.
Phosphate presence in rivers, lakes and streams is mainly attributed to treated sewage water and run-off from agricultural land.
Rob added: “Phosphate readily ‘sticks’ to other particles such as silt and sediment which transports it downstream.
“Under the right conditions, the nutrient becomes very reactive in water and is taken up by plants and algae which then grow quickly and excessively.
“Too much algae and vegetation stop essential processes within the river’s ecosystem and can cause water quality to decline.
“Excess vegetation also reduces the size of the river channel and can cause issues for boating, fishing and flood risk management.”
The sampling work is important because it will identify the amount of phosphate stored in sediment. The results will help to determine whether trials to remove phosphate-bound silt should be considered to meet the requirements of the Water Framework Directive.
The Water Framework Directive aims to ensure the River Nene meets good ecological status by 2027.
The Environment Agency is already working with farmers to reduce agricultural sources of phosphate through the catchment sensitive farming programme.
Catchment Sensitive Farming (CSF) delivers practical solutions and targeted support to help farmers and land managers take voluntary action to reduce water pollution from agriculture.
Work is also being carried out with water companies to improve the treatment of effluent through infrastructure improvements.
The survey, which will cost £46,000, started in January and the final report is due to be completed in June.