A multimillion pound investment in a sewage treatment plant will boost a river’s water quality, Southern Water has said.

The company said three major projects worth £7.3 million at the Barcombe site will help improve the ecology of streams feeding the River Ouse, cut storm overflows into it and increase capacity to handle expected population growth in the area.

About £4 million has been spent on a system which removes phosphates from the treated final effluent. Phosphates cause algal bloom and lead to the choking of rivers and damage to the ecosystem and habitats.

Barcombe is one of 110 sites where processes to take phosphates out have been installed in recent years to support the Environment Agency’s work to prevent such chemicals, also including nitrate fertilisers, affecting river health.

Almost £2 million is also going towards the construction of a new glass-coated steel storm tank, which will help the site cope when surface water overloads the network following prolonged rainfall events. The new tank will hold 300 tonnes of stormwater, before allowing it to re-enter the full treatment process when volumes drop.

The capacity of the site has increased from 20.8 litres a second being treated to 32.3 litres a second.

John Penicud, director of wastewater operations at Southern Water, said: “There are many contributors to river health – including farming – but we know we have a key part to play too. We are investing in projects like this across the region to deliver real tangible benefits to customers and the environment.”